Optical disk having wobble patterns

ABSTRACT

On an optical disk medium according to the present invention, address information is recorded along a wobbling track groove  2.  The track groove  2  is made up of a plurality of unit sections  22, 23.  Each of these unit sections  22, 23  has side faces that are displaced periodically in a disk radial direction. This displacement oscillates at a single period in a tracking direction. However, the displacement pattern differs depending on “each bit of address information (subdivided information)” allocated to each of the unit sections  22, 23.

This is a continuation of International Application PCT/JP01/07502, withan international filing date of Aug. 30, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disk on which information(e.g., digital video information) can be stored at a high density.

2. Description of the Related Art

In recent years, the recording density of optical disk media goes onincreasing. On an optical disk medium, a track groove has normally beenformed in advance and a recording film has been formed so as to coverthe track groove. Data or information is written by the user on therecording film along the track groove, i.e., either on the track grooveor on an area (land) interposed between adjacent parts of the trackgroove.

The track groove is formed so as to wobble just like a sine wave and aclock signal is generated in accordance with a wobble period.Synchronously with this clock signal, user data is written on, or readout from, the recording film.

To write data at a predetermined position on an optical disk, addressinformation (positional information), indicating physical locations onthe optical disk, needs to be allocated to, and recorded at, respectivesites on the optical disk while the disk is being manufactured.Normally, an address is allocated to a series of areas that are arrangedalong a track groove and have a predetermined length. There are variousmethods for recording such address information on an optical disk.Hereinafter, a conventional method for recording an address on anoptical disk will be described.

Japanese Laid-Open Publication No. 6-309672 discloses a disk storagemedium on which a wobbling track groove is discontinued locally so thatan address-dedicated area is provided for the discontinued part.Pre-pits, representing address information recorded, are formed on theaddress-dedicated area on the track groove. This optical disk has astructure in which the address-dedicated area and a data-dedicated area(for writing information thereon) coexist on the same track groove.

Japanese Laid-Open Publication No. 5-189934 discloses an optical disk onwhich address information is recorded by changing the wobble frequencyof a track groove. In an optical disk like this, an area on which theaddress information is recorded and an area on which data will bewritten are not separated from each other along the track.

Japanese Laid-Open Publication No. 9-326138 discloses an optical disk onwhich pre-pits are formed between adjacent parts of a track groove.These pre-pits represent the address information recorded.

These various types of optical disks have the following problems to besolved for the purpose of further increasing the recording density.

First, as for the optical disk on which address information is recordedas pre-bits within the address-dedicated area on the track, a so-called“overhead” occurs to secure the address-dedicated area and the data areashould be reduced disadvantageously. As a result, the storage capacityavailable for the user has to be reduced.

Next, as for the optical disk for recording an address thereon bymodulating the wobble frequency of the track, a write clock signalcannot be generated precisely enough. Originally, the wobble of thetrack groove is created mainly to generate a clock signal forestablishing synchronization required for read and write operations.Where the wobble frequency is single, a clock signal can be generatedhighly precisely by getting a read signal, having amplitude changingwith the wobble, synchronized and multiplied by a PLL, for example.However, if the wobble frequency is not single but has multiplefrequency components, then the frequency band that the PLL can follow upshould be lowered (as compared to the situation where the wobble has asingle frequency) to avoid pseudo locking of the PLL. In that case, thePLL cannot sufficiently follow up the jitter of a disk motor or a jitterresulting from the eccentricity of a disk. Thus, some jitter mightremain in the resultant recording signal.

On the other hand, where the recording film formed on the optical diskis a phase-change film, for example, such a recording film may result ina decreased SNR as the data stored on the film is altered repeatedly. Ifthe wobble frequency is single, the noise components are removable usinga band-pass filter having a narrow band. However, if the wobblefrequency has been modulated, the filter should have its bandwidthbroadened. As a result, the noise components are much more likelycontained and the jitter might be further worsened. It is expected thatthe recording density will be further increased from now on. However,the higher the recording density, the narrower the allowable jittermargin will get. Accordingly, it will be more and more necessary tominimize the increase in jitter by avoiding the modulation of the wobblefrequency.

In the structure in which the pre-pits representing the addressinformation recorded are formed between adjacent parts of the groove, itis difficult to form long enough pre-pits in sufficiently large numbers.Accordingly, as the recording density is increased, detection errorsmight increase its number. This is because if large pre-pits are formedbetween adjacent parts of the groove, then those pits will affectadjacent parts of the track.

In order to solve the problems described above, a main object of thepresent invention is to provide an optical disk medium that contributesto minimizing the overhead and generating a clock signal preciselyenough in accordance with the wobble of the track groove.

Another object of this invention is to provide a method and apparatusfor reading an address that has been recorded on the optical diskmedium.

SUMMARY OF THE INVENTION

An optical disk medium according to the present invention includes atrack groove. On the optical disk medium, information is recorded alongthe track groove. The track groove includes a plurality of unit sectionsthat are arranged along the track groove and that have side facesdisplaced periodically along the track groove. The side faces of theunit sections are displaced in a single fundamental period. Subdividedinformation allocated to each said unit section is represented by ashape given to the unit section.

In a preferred embodiment, the side faces of the track groove aredisplaced either toward inner or outer periphery of the disk withrespect to a centerline of the track groove.

In another preferred embodiment, the information is recorded on ablock-by-block basis. Each said block has a predetermined length andincludes a number N of unit sections that are arranged along the trackgroove.

In another preferred embodiment, part of the side faces that is sharedby at least two of the unit sections has a constant displacement periodwithin at least one of the blocks.

In another preferred embodiment, one-bit subdivided information isallocated to each said unit section, and a group of subdividedinformation representing N bits is recorded on the N unit sections thatare included in each said block.

In another preferred embodiment, each said N-bit subdivided informationgroup includes address information of its associated block to which theunit sections, where the subdivided information group is recorded,belong.

In another preferred embodiment, each said N-bit subdivided informationgroup includes an error correction code and/or an error detection code.

In another preferred embodiment, the error correction code or the errordetection code has its ability to correct an error of the addressinformation weighted in such a manner that low-order bits of the errorcorrection or detection code have a relatively large weight.

In another preferred embodiment, each said unit section has a first sidedisplacement pattern that has been so defined as to make a signalwaveform rise relatively steeply and fall relatively gently or a secondside displacement pattern that has been so defined as to make a signalwaveform rise relatively gently and fall relatively steeply.

An inventive address reading method is a method for reading subdividedinformation from an optical disk medium, which includes a track grooveand on which information is recorded along the track groove. The trackgroove includes a plurality of unit sections that are arranged along thetrack groove and that have side faces displaced periodically along thetrack groove. The side faces of the unit sections are displaced in asingle fundamental period. The subdivided information allocated to eachsaid unit section is represented by a shape given to the unit section.The side faces of each said unit section are displaced according to apattern to be selected from first and second wobble patterns that havethe same fundamental frequency but mutually different shapes. In thismethod, the subdivided information allocated to each said unit sectionis identified by comparing a number of times the first wobble patternhas been detected from the unit section with a number of times thesecond wobble pattern has been detected from the unit section.

In a preferred embodiment, if a difference between the number of timesthe first wobble pattern has been detected from each said unit sectionand the number of times the second wobble pattern has been detected fromthe unit section falls within a predetermined range, then the subdividedinformation allocated to the unit section is error-corrected.

In another preferred embodiment, a type of a given wobble pattern isidentified by a gradient of a leading or trailing edge of a signalcorresponding to the wobble pattern.

In another preferred embodiment, the type of the given wobble pattern isidentified by comparing an absolute gradient value of the leading edgeof the signal to an absolute gradient value of the trailing edgethereof.

An optical disk reproducing apparatus according to the present inventionis an apparatus for reading subdivided information from an optical diskmedium, which includes a track groove and on which information isrecorded along the track groove. The track groove includes a pluralityof unit sections that are arranged along the track groove and that haveside faces displaced periodically along the track groove. The side facesof the unit sections are displaced in a single fundamental period. Thesubdivided information allocated to each said unit section isrepresented by a shape given to the unit section. The side faces of eachsaid unit section are displaced according to a pattern to be selectedfrom first and second wobble patterns that have the same fundamentalfrequency but mutually different shapes. The apparatus includes: anoptical head, which irradiates the optical disk medium with light andgenerates an electric signal responsive to part of the light that beenreflected from the optical disk medium; read signal processing means forgenerating a wobble signal, which has amplitude changing with the wobblepattern, from the electric signal; rise value acquiring means forsampling and holding an absolute gradient value of the wobble signalwhen the signal rises; fall value acquiring means for sampling andholding an absolute gradient value of the wobble signal when the signalfalls; and subdivided information detecting means for determining thesubdivided information by majority by comparing the values held by therise and fall value acquiring means with each other.

Another optical disk reproducing apparatus according to the presentinvention is an apparatus for reading subdivided information from anoptical disk medium, which includes a track groove and on whichinformation is recorded along the track groove. The track grooveincludes a plurality of unit sections that are arranged along the trackgroove and that have side faces displaced periodically along the trackgroove. The side faces of the unit sections are displaced in a singlefundamental period. The subdivided information allocated to each saidunit section is represented by a shape given to the unit section. Theside faces of each said unit section are displaced according to apattern to be selected from first and second wobble patterns that havethe same fundamental frequency but mutually different shapes. Theapparatus includes: an optical head, which irradiates the optical diskmedium with light and generates an electric signal responsive to part ofthe light that been reflected from the optical disk medium; read signalprocessing means for generating a wobble signal, which has amplitudechanging with the wobble pattern, from the electric signal; timinggenerating means for generating a timing signal that defines a timing atwhich the wobble signal rises, a timing at which the wobble signal fallsand a timing at which the subdivided information is sectioned; firstshape counting means for detecting the first wobble pattern responsiveto the timing signal and counting the number of times the first wobblepattern has been detected; second shape counting means for detecting thesecond wobble pattern responsive to the timing signal and counting thenumber of times the second wobble pattern has been detected; andsubdivided information detecting means for determining the subdividedinformation by majority by comparing counts of the first and secondshape counting means with each other.

Another optical disk reproducing apparatus according to the presentinvention is an apparatus for reading subdivided information from anoptical disk medium, which includes a track groove and on whichinformation is recorded along the track groove. The track grooveincludes a plurality of unit sections that are arranged along the trackgroove and that have side faces displaced periodically along the trackgroove. The side faces of the unit sections are displaced in a singlefundamental period. The subdivided information allocated to each saidunit section is represented by a shape given to the unit section. Theside faces of each said unit section are displaced according to apattern to be selected from first and second wobble patterns that havethe same fundamental frequency but mutually different shapes. Theapparatus includes: an optical head, which irradiates the optical diskmedium with light and generates an electric signal responsive to part ofthe light that been reflected from the optical disk medium; read signalprocessing means for generating a wobble signal, which has amplitudechanging with the wobble pattern, from the electric signal; timinggenerating means for generating a timing signal that defines a timing atwhich the wobble signal rises, a timing at which the wobble signal fallsand a timing at which the subdivided information is sectioned; firstshape counting means for detecting the first wobble pattern responsiveto the timing signal and counting the number of times the first wobblepattern has been detected; second shape counting means for detecting thesecond wobble pattern responsive to the timing signal and counting thenumber of times the second wobble pattern has been detected; subdividedinformation detecting means for determining the subdivided informationby majority by comparing counts of the first and second shape countingmeans with each other; erasure detecting means for outputting an erasureflag if a difference between the counts of the first and second shapecounting means falls within a predetermined range; and error correctingmeans for conducting error correction in accordance with outputs of thesubdivided information detecting means and the erasure detecting meansand generating address information.

Another optical disk medium according to the present invention includesa track groove. On the optical disk medium, positional informationindicating a physical location on the track groove is represented by awobble shape of the track groove. The optical disk medium includes aplurality of positional information units that are arranged on the trackgroove. Each said positional information unit includes: a positionalinformation section that represents the positional information by acombination of wobble patterns selected from multiple types of wobblepatterns; and a sync mark section having a wobble pattern in a shapedistinguishable from the wobble patterns of the positional informationsection.

In a preferred embodiment, the optical disk medium includes a precisionpositioning mark section ahead of each said positional informationsection.

In another preferred embodiment, the precision positioning mark sectionis disposed at the beginning of each said positional information unit.

In another preferred embodiment, the precision positioning mark sectionhas a wobble pattern in a shape distinguishable from the wobble patternof the sync mark section.

In another preferred embodiment, the precision positioning mark sectionhas a wobble pattern in a shape distinguishable from the wobble patternsof the positional information section.

In another preferred embodiment, each said wobble pattern in thepositional information section includes: a first part having a smoothsine wave shape; and a second part in which adisk-inner-periphery-oriented displacement and/or adisk-outer-periphery-oriented displacement have/has a shape steeper thanthe part having the sine wave shape.

In another preferred embodiment, the wobble pattern in the sync marksection includes the first part and/or the second part.

In another preferred embodiment, the precision positioning mark sectionincludes an identification mark for use in precision positioning.

In another preferred embodiment, the identification mark is a mirrormark that has been formed by discontinuing a part of the track groove.

In another preferred embodiment, the mirror mark is disposed at thesecond through fourth period parts of the wobble pattern in theprecision positioning mark section.

In another preferred embodiment, the wobble pattern in the precisionpositioning mark section has a sine wave shape.

In another preferred embodiment, in each said positional informationunit, the precision positioning mark section, the positional informationsection and the sync mark section are arranged in this order.

In another preferred embodiment, a recording block, which is a smallestread/write unit, includes a number L of the positional information units(where L is a natural number).

In another preferred embodiment, the recording block corresponds to adata unit that constitutes an error correction code.

In another preferred embodiment, writing on the recording block iseither started or ended behind a start point of the precisionpositioning mark section by a predetermined length.

In another preferred embodiment, writing on the recording block iseither started or ended behind the mirror mark by a predeterminedlength.

In another preferred embodiment, the mirror mark has a length of 1 μm to10 μm as measured along the track groove.

In another preferred embodiment, a single subdivided information unit isrepresented by a wobble for M periods (where M is a natural number equalto or greater than 2), and one bit of the positional information isallocated to each said subdivided information unit.

In another preferred embodiment, the sync mark section is a combinationof first and second wobble patterns, the number of which is N (which isa natural number). In each said first wobble pattern, a wobble, havingrectangular parts in which disk-inner-periphery-oriented anddisk-outer-periphery-oriented displacements are both steep, is repeatedfor a number M of periods. In each said second wobble pattern, a smoothsine wave wobble is repeated for the M periods.

In another preferred embodiment, the sync mark section is made up of thefirst wobble patterns only.

In another preferred embodiment, the first and second wobble patternsare arranged alternately in the sync mark section.

In another preferred embodiment, the sync mark section is a combinationincluding both a transition point from the first wobble pattern into thesecond wobble pattern and a transition point from the second wobblepattern into the first wobble pattern.

In another preferred embodiment, supposing the positional information isrepresented by A bits; the sync mark section has a length correspondingto B wobble periods; the precision positioning mark section, includingthe mirror mark, has a length corresponding to C wobble periods; onewobble period has a length corresponding to W channel bits of recordingdata; the number of channel bits of a recording block, which is asmallest read/write unit, is D; and the number of the positionalinformation units allocated to each said recording block is E, where A,B, C, E, M and W are all natural numbers, an equation D=(A×M+B+C)×W×E issatisfied.

In another preferred embodiment, B is a multiple of M.

In another preferred embodiment, A=48, M=32, B=128, C=8, W=186 and E=4.

In another preferred embodiment, A=48, M=36, B=144, C=9, W=155 and E=4.

In another preferred embodiment, A=48, M=24, B=96, C=6, W=186 and E=4.

In another preferred embodiment, A=48, M=36, B=144, C=9, W=124 and E=4.

The optical disk medium may use a modulation code for converting 8 bitsinto F channel bits. Supposing the precision positioning mark section,including the mirror mark, has a length corresponding to C wobbleperiods; one wobble period has a length corresponding to W channel bitsof recording data; the precision positioning mark section has a lengthcorresponding to P frames of the recording data; one subdividedinformation unit has a length corresponding to Q frames of the recordingdata; and one frame of the recording data has a number R of bytes, whereC, F, W and R are natural numbers and P and Q are rational numbers,equations P×R×F=C×W and Q×R×F=M×W are both satisfied.

In a preferred embodiment, F=16, M=32, C=8, W=186, P=1, Q=4 and R=93.

In another preferred embodiment, F=15, M=36, C=9, W=155, P=1, Q=4 andR=93.

In another preferred embodiment, F=12, M=24, C=6, W=186, P=1, Q=4 andR=93.

In another preferred embodiment, F=12, M=36, C=9, W=124, P=1, Q=4 andR=93.

An inventive positional information reading method is a method forreading out positional information from the optical disk medium of thepresent invention. The method includes the steps of: detecting the syncmark section that has been formed on the optical disk medium; detectingthe precision positioning mark; establishing a bit synchronization forthe positional information using the sync mark detected and/or theprecision positioning mark detected; and reading out the positionalinformation in accordance with the bit synchronization established inthe step of establishing the bit synchronization for the positionalinformation.

An inventive data writing method is a method for writing data on theoptical disk medium of the present invention. The method includes thesteps of: detecting the sync mark section that has been formed on theoptical disk medium; detecting the precision positioning mark based onthe sync mark section detected; performing positioning using theprecision positioning mark detected; and starting to write the databased on a positioning result obtained in the positioning step.

An optical disk reproducing apparatus according to the present inventionis an apparatus for reading out positional information from the opticaldisk medium of the present invention. The drive includes: means fordetecting the sync mark section that has been formed on the optical diskmedium; means for generating a first detection window with apredetermined time width after a predetermined time has passed since atiming at which the sync mark was detected by the sync mark detectingmeans; means for detecting the identification mark, which has beenformed on the optical disk medium, by using the first detection window;means for establishing a bit synchronization for the positionalinformation, which is recorded on the optical disk medium, by using thetiming at which the sync mark has been detected and/or a timing at whichthe identification mark has been detected; and means for reading out thepositional information at a timing at which the bit synchronization hasbeen established by the means for establishing the bit synchronizationfor the positional information.

An optical disk recording apparatus according to the present inventionis an apparatus for writing data on the optical disk medium of thepresent invention. The drive includes: means for detecting the sync marksection that has been formed on the optical disk medium; means forgenerating a first detection window with a predetermined time widthafter a predetermined time has passed since a timing at which the syncmark was detected by the sync mark detecting means; means for detectingthe identification mark, which has been formed on the optical diskmedium, by using the first detection window; and data writing means forsetting a data writing start point or end point by reference to a timingat which the identification mark has been detected.

Another optical disk medium according to the present invention includesa track groove. On the optical disk medium, information is recordedalong the track groove. The track groove includes a plurality of unitsections that are arranged along the track groove and that have sidefaces displaced periodically along the track groove. The side faces ofthe unit sections are displaced in a common period. Subdividedinformation allocated to each said unit section is represented by ashape given to the unit section. On this optical disk medium, controlinformation is represented by a combination of the subdividedinformation.

In a preferred embodiment, the control information is recorded on anon-user area.

Another optical disk medium according to the present invention includesa track groove. On the optical disk medium, information is recordedalong the track groove. Management information of the optical diskmedium is represented by wobbling of the track groove.

In a preferred embodiment, the control information is represented by acombination of mutually different wobble waveforms that oscillate at thesame frequency.

In another preferred embodiment, the control information is representedby a combination of wobble shapes including: a smooth sine wave part;and a rectangular part in which a disk-inner-periphery-orienteddisplacement and/or a disk-outer-periphery-oriented displacement are/issteep.

Another optical disk medium according to the present invention includesa track groove on a recording surface thereof. On the optical diskmedium, information is recorded along the track groove on the basis of ablock unit having a predetermined length. An identification mark,indicating the beginning of each said block unit, has been formed on thetrack groove. A signal having a particular pattern is overwritten on theidentification mark.

In a preferred embodiment, the identification mark is locatedsubstantially at the center of an area on which the signal is written.

In another preferred embodiment, the identification mark is locatedcloser to a previous block with respect to the center of an area onwhich the signal is written.

In another preferred embodiment, the identification mark includes a flatportion that has been formed by discontinuing the track groove for ashort interval.

In another preferred embodiment, the identification mark includes aplurality of sub-marks.

In another preferred embodiment, the track groove wobbles periodically.The identification mark is formed by connecting together a plurality ofareas of the track groove that have mutually different wobble phases.

In another preferred embodiment, the track groove is provided with aperiodic wobble. The identification mark has a frequency different froma frequency of the wobble.

In another preferred embodiment, each said block unit having thepredetermined length includes a plurality of sub-blocks that arearranged along the groove. A sub-block identification mark is providedwithin each said sub-block.

In another preferred embodiment, the track groove is provided with aperiodic wobble. A wobble having a frequency different from that of theother parts is allocated to each said sub-block identification mark.

In another preferred embodiment, each said sub-block identification markis located at the beginning of its associated sub-block.

In another preferred embodiment, the identification mark for one of thesub-blocks included in each said block unit having the predeterminedlength represents subdivided information indicating an address of theblock unit.

In another preferred embodiment, the wobble of the track groove has ashape corresponding to the information indicating the address of eachsaid block unit.

An inventive signal writing method is a method for writing a signal onan optical disk medium including a track groove on a recording surfacethereof. On the optical disk medium, information is recorded along thetrack groove on the basis of a block unit having a predetermined length,and an identification mark, indicating the beginning of each said blockunit, has been formed on the track groove. Writing is started before theidentification mark, located at the beginning of at least one block uniton which the signal should be written, is reached. The writing is endedafter the identification mark, located at the end of the at least oneblock unit on which the signal should be written, has been passed.

Another inventive signal writing method is a method for writing a signalon an optical disk medium including a track groove on a recordingsurface thereof. On the optical disk medium, information is recordedalong the track groove on the basis of a block unit having apredetermined length. An identification mark, indicating the beginningof each said block unit and including a plurality of sub-marks, has beenformed on the track groove. Writing is started after the first one ofthe sub-marks, included in the identification mark located at thebeginning of at least one block unit on which the signal should bewritten, has been detected. The writing is ended after the last one ofthe sub-marks, included in the identification mark located at the end ofthe at least one block unit on which the signal should be written, hasbeen detected.

In a preferred embodiment, a signal having a particular pattern isoverwritten on each said identification mark.

In another preferred embodiment, the signal having the particularpattern is a VFO signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of an optical disk medium according to thepresent invention.

FIG. 1B is a plan view illustrating a planar shape of a track groove onthe optical disk medium of the present invention.

FIG. 2(a) illustrates plan views showing wobble pattern elements, whileFIG. 2(b) illustrates plan views showing four types of wobble patternsformed by combining those elements.

FIG. 3A illustrates a basic configuration for an apparatus that canidentify the type of a given wobble pattern by a wobble signal havingamplitude changing with the wobble of a track groove.

FIG. 3B illustrates waveform diagrams showing a wobble pattern of thetrack groove, the wobble signal and a pulse signal.

FIG. 3C illustrates a circuit configuration for extracting the pulsesignal and a clock signal from the wobble signal.

FIG. 4 illustrates a main portion of an optical disk medium according toa first embodiment.

FIG. 5 illustrates a configuration for an optical disk reproducingapparatus according to a second embodiment.

FIG. 6 illustrates a configuration for an optical disk reproducingapparatus according to a third embodiment.

FIG. 7 illustrates an address reading method according to a fourthembodiment.

FIG. 8 illustrates a configuration for an optical disk reproducingapparatus according to a fifth embodiment.

FIG. 9 illustrates a detailed configuration for a wobble shape detectingmeans according to the fifth embodiment.

FIG. 10 illustrates a main portion of an optical disk medium accordingto a sixth embodiment.

FIGS. 11A and 11B illustrate a method for writing a signal on a VFOrecording area 21.

FIG. 12 illustrates a main portion of an optical disk medium accordingto a seventh embodiment.

FIG. 13 illustrates a main portion of an optical disk medium accordingto an eighth embodiment.

FIGS. 14A and 14B illustrate a signal writing method according to theeighth embodiment.

FIG. 15 illustrates a main portion of an optical disk medium accordingto a ninth embodiment.

FIG. 16 illustrates a main portion of an optical disk medium accordingto a tenth embodiment.

FIG. 17 illustrates a main portion of an optical disk medium accordingto an eleventh embodiment.

FIG. 18 illustrates a main portion of an optical disk medium accordingto a twelfth embodiment.

FIG. 19 illustrates a configuration for an apparatus for generating aclock signal and reading an address signal from the optical disk mediumof the twelfth embodiment.

FIG. 20 illustrates a format for a group of subdivided information on anoptical disk medium according to a thirteenth embodiment.

FIG. 21 illustrates a format for a group of subdivided information on anoptical disk medium according to a fourteenth embodiment.

FIG. 22 illustrates a format for a group of subdivided information on anoptical disk medium according to a fifteenth embodiment.

FIG. 23 illustrates respective bits for the group of subdividedinformation on the optical disk medium of the fifteenth embodiment.

FIGS. 24(a) through 24(d) illustrate a format for an optical disk mediumaccording to a sixteenth embodiment.

FIG. 25 illustrates a detailed format for the optical disk mediumaccording to the sixteenth embodiment.

FIGS. 26A through 26D schematically illustrate a track groove of theoptical disk medium according to the sixteenth embodiment.

FIG. 27 illustrates a precision positioning mark section of the opticaldisk medium according to the sixteenth embodiment.

FIGS. 28A through 28E illustrate formats for the sync mark section ofthe optical disk medium according to the sixteenth embodiment.

FIG. 29 illustrates a configuration for an optical disk read/write driveaccording to a seventeenth embodiment.

FIGS. 30A through 30E illustrate positional relationships betweenwriting start/end points and mirror marks according to an eighteenthembodiment.

FIGS. 31A through 31C illustrate exemplary recording data formatsaccording to the eighteenth embodiment.

FIGS. 32(a) through 32(c) illustrate an exemplary method for writingdata at writing start/end points in accordance with the eighteenthembodiment.

FIG. 33 is a flowchart illustrating the flow of exemplary positionalinformation reading processing according to the eighteenth embodiment.

FIG. 34 is a flowchart illustrating the flow of another exemplarypositional information reading processing according to the eighteenthembodiment.

FIG. 35 is a flowchart illustrating the flow of exemplary data writeprocess according to the eighteenth embodiment.

FIG. 36 illustrates a format for an optical disk medium according to theeighteenth embodiment.

FIGS. 37A through 37E illustrate other exemplary recording formats forcontrol information according to a nineteenth embodiment.

FIG. 38 illustrates an embodiment in which four positional informationunits, included in one positional information segment 403, includepositional information and control information separately.

FIG. 39 illustrates a configuration for an optical disk read/write drivethat can read the control information recorded by the wobble of agroove.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As shown in FIG. 1A, a spiral track groove 2 has been formed on therecording surface 1 of an optical disk medium according to the presentinvention. FIG. 1B illustrates a part of the track groove 2 to a largerscale. In FIG. 1B, a disk center (not shown) exists below the trackgroove 2 and a disk radial direction is indicated by the arrow a. Thearrow b points a direction in which a read/write light beam spot, beingformed on the disk, moves as the disk is rotated. In the followingdescription, a direction parallel to the arrow a will be herein referredto as a “disk radial direction” (or “radial direction” simply), while adirection parallel to the arrow b will be herein referred to as a“tracking direction”.

In a coordinate system in which the light beam spot is supposed to beformed at a fixed position on the disk, a part of the disk irradiatedwith the light beam (which will be herein referred to as a “diskirradiated part”) moves in the direction opposite to the arrow b.

Hereinafter, the X-Y coordinate system illustrated in FIG. 1B will beconsidered. In an optical disk according to the present invention, the Ycoordinate of a position on a side face 2 a or 2 b of the track groovechanges periodically as the X coordinate thereof increases. Such aperiodic positional displacement on the groove side face 2 a or 2 b willbe herein referred to as the “wobble” or “wobbling” of the track groove2. A displacement in the direction pointed by the arrow a will be hereinreferred to as a “disk-outer-periphery-oriented displacement”, while adisplacement in the direction opposite to the arrow a will be hereinreferred to as a “disk-inner-periphery-oriented displacement”. Also, inFIG. 1B, one wobble period is identified by “T”. The wobble frequency isinversely proportional to one wobble period T and is proportional to thelinear velocity of the light beam spot on the disk.

In the illustrated example, the width of the track groove 2 is constantin the tracking direction (as indicated by the arrow b). Accordingly,the amount to which a position on the side face 2 a or 2 b of the trackgroove 2 is displaced in the disk radial direction (as indicated by thearrow a) is equal to the amount to which a corresponding position on thecenterline of the track groove 2 (as indicated by the dashed line) isdisplaced in the disk radial direction. For this reason, thedisplacement of a position on the side face of the track groove in thedisk radial direction will be herein simply referred to as the“displacement of the track groove” or the “wobble of the track groove”.It should be noted, however, that the present invention is not limitedto this particular situation where the centerline and the side faces 2 aand 2 b of the track groove 2 wobble to the same amount in the diskradial direction. Alternatively, the width of the track groove 2 maychange in the tracking direction. Or the centerline of the track groove2 may not wobble but only the side faces of the track groove may wobble.

In the present invention, the wobbling structure of the track groove 2is defined as a combination of multiple types of displacement patterns.That is to say, the planar shape of the track groove 2 does not consistof just the sine waveform shown in FIG. 1B but at least part of it has ashape different from the sine waveform. A basic configuration for such awobbled groove is disclosed in the descriptions of Japanese PatentApplication Nos. 2000-6593, 2000-187259 and 2000-319009 that were filedby the present applicant.

As for the track groove 2 shown in FIG. 1B, the Y coordinate of aposition on the centerline of the groove may be represented by afunction f₀(x) of the X coordinate thereof. In that case, f₀(x) may begiven by “constant·sin (2πx/T)”, for example.

Hereinafter, the configurations of wobble patterns adopted in thepresent invention will be described in detail with reference to FIGS.2(a) and 2(b).

FIG. 2(a) illustrates the four types of basic elements that make up awobble pattern of the track groove 2. In FIG. 2(a), smooth sine waveformportions 100 and 101, a rectangular portion 102 with a steepdisk-outer-periphery-oriented displacement and a rectangular portion 103with a steep disk-inner-periphery-oriented displacement are shown. Bycombining these elements or portions with each other, the four types ofwobble patterns 104 through 107 shown in FIG. 2(b) are formed.

The wobble pattern 104 is a sine wave with no rectangular portions. Thispattern will be herein referred to as a “fundamental waveform”. Itshould be noted that the “sine wave” is not herein limited to a perfectsine curve, but may broadly refer to any smooth wobble.

The wobble pattern 105 includes portions that are displaced toward thedisk outer periphery more steeply than the sine waveform displacement.Such portions will be herein referred to as “outer-periphery-orienteddisplaced rectangular portions”.

In an actual optical disk, it is difficult to realize the displacementof a track groove in the disk radial direction vertically to thetracking direction. Accordingly, an edge actually formed is notperfectly rectangular. Thus, in an actual optical disk, an edge of arectangular portion may be displaced relatively steeply compared to asine waveform portion and does not have to be perfectly rectangular. Ascan also be seen from FIG. 2(b), at a sine waveform portion, adisplacement from the innermost periphery toward the outermost peripheryis completed in a half wobble period. As for a rectangular portion, asimilar displacement may be finished in a quarter or less of one wobbleperiod, for example. Then, the difference between these shapes is easilydistinguishable.

It should be noted that the wobble pattern 106 is characterized byinner-periphery-oriented displaced rectangles while the wobble pattern107 is characterized by both “inner-periphery-oriented displacedrectangles” and “outer-periphery-oriented displaced rectangles”.

The wobble pattern 104 consists of the fundamental waveform alone.Accordingly, the frequency components thereof are defined by a“fundamental frequency” that is proportional to the inverse number ofthe wobble period T. In contrast, the frequency components of the otherwobble patterns 105 through 107 include not only the fundamentalfrequency components but also high-frequency components. Thosehigh-frequency components are generated by the steep displacements atthe rectangular portions of the wobble patterns.

If the coordinate system shown in FIG. 1B is adopted for each of thesewobble patterns 105 through 107 to represent the Y coordinate of aposition on the track centerline by a function of the X coordinatethereof, then the function may be expanded into Fourier series. Theexpanded Fourier series will include a term of a sin function having anoscillation period shorter than that of sin (2πx/T), i.e., a harmoniccomponent. However, each of these wobble patterns includes a fundamentalwave component. The frequency of the fundamental waveform will be hereinreferred to as a “wobble frequency”. The four types of wobble patternsdescribed above have a common wobble frequency.

In the present invention, instead of writing address information on thetrack groove 2 by modulating the wobble frequency, the multiple types ofwobble patterns are combined with each other, thereby recording varioustypes of information, including the address information, on the trackgroove. More specifically, by allocating one of the four types of wobblepatterns 104 through 107 to each predetermined section of the trackgroove, four types of codes (e.g., “B”, “S”, “0” and “1”, where “B”denotes block information, “S” denotes synchronization information and acombination of zeros and ones represents an address number or an errordetection code thereof) may be recorded.

Next, the fundamentals of an inventive method for reading information,which has been recorded by the wobble of the track groove, from theoptical disk will be described with reference to FIGS. 3A and 3B.

First, FIGS. 3A and 3B will be referred to.

FIG. 3A illustrates a main portion of a reproducing apparatus, whileFIG. 3B illustrates a relationship between the track groove and a readsignal.

The track groove 200 schematically illustrated in FIG. 3B is scanned bya read laser beam 201 so that the spot thereof moves in the arroweddirection. The laser beam 201 is reflected from the optical disk to formreflected light 202, which is received at detectors 203 and 204 of thereproducing apparatus shown in FIG. 3A. The detectors 203 and 204 arespaced apart from each other in a direction corresponding to the diskradial direction and each output a voltage corresponding to theintensity of the light received. If the position at which the detectors203 and 204 are irradiated with the reflected light 202 (i.e., theposition at which the light is received) shifts toward one of thedetectors 203 and 204 with respect to the centerline that separates thedetectors 203 and 204 from each other, then a difference is createdbetween the outputs of the detectors 203 and 204 (which is “differentialpush-pull detection”). The outputs of the detectors 203 and 204 areinput to a differential circuit 205, where a subtraction is carried outon them. As a result, a signal corresponding to the wobble shape of thegroove 200 (i.e., a wobble signal 206) is obtained. The wobble signal206 is input to, and differentiated by, a high-pass filter (HPF) 207. Asa result, the smooth fundamental components that have been included inthe wobble signal 206 are attenuated and instead a pulse signal 208,including pulse components corresponding to rectangular portions withsteeps gradients, is obtained. As can be seen from FIG. 3B, the polarityof each pulse in the pulse signal 208 depends on the direction of itsassociated steep displacement of the groove 200. Accordingly, the wobblepattern of the groove 200 is identifiable by the pulse signal 208.

Next, referring to FIG. 3C, illustrated is an exemplary circuitconfiguration for generating the pulse signal 208 and a clock signal 209from the wobble signal 206 shown in FIG. 3B.

In the exemplary configuration illustrated in FIG. 3C, the wobble signal206 is input to first and second band-pass filters BPF1 and BPF2, whichgenerate the pulse and clock signals 208 and 209, respectively.

Supposing the wobble frequency of the track is fw (Hz), the firstband-pass filter BPF1 may be a filter having such a characteristic thatthe gain (i.e., transmittance) thereof reaches its peak at a frequencyof 4 fw to 6 fw (e.g., 5 fw). In a filter like this, the gain thereofpreferably increases at a rate of 20 dB/dec, for example, in a rangefrom low frequencies to the peak frequency, and then decreases steeply(e.g., at a rate of 60 dB/dec) in a frequency band exceeding the peakfrequency. In this manner, the first band-pass filter BPF1 canappropriately generate the pulse signal 208, representing therectangularly changing portions of the track wobble, from the wobblesignal 206.

On the other hand, the second band-pass filter BPF2 has such a filteringcharacteristic that the gain thereof is high in a predeterminedfrequency band (e.g., in a band ranging from 0.5 fw to 1.5 fw andincluding the wobble frequency fw at the center) but is small at theother frequencies. The second band-pass filter BPF2 like this cangenerate a sine wave signal, having a frequency corresponding to thewobble frequency of the track, as the clock signal 209.

Hereinafter, embodiments of the optical disk medium of the presentinvention will be described in detail.

Embodiment 1

A spiral track groove 2 such as that shown in FIG. 1A is also formed onthe recording surface 1 of an optical disk according to this embodiment.

FIG. 4 illustrates the shape of the track groove 2 of this embodiment.The track groove 2 is divided into a plurality of blocks, and a blockmark (identification mark) 210 for use as a positioning mark is providedbetween two adjacent blocks. The block mark 210 of this embodiment isformed by discontinuing the track groove 2 for just a short length.

The track groove 2 includes a plurality of unit sections 22, 23, andeach block is made up of a predetermined number of unit sections 22, 23.An arbitrary wobble pattern, selected from a plurality of wobblepatterns, may be allocated to each unit section. In the exampleillustrated in FIG. 4, the wobble patterns 106 and 105 shown in FIG.2(b) are allocated to the unit sections 22 and 23, respectively.

Each of these wobble patterns 105 and 106 carries a one-bit informationelement (i.e., “0” or “1”), which will be herein referred to as“subdivided information”. By identifying the type of the wobble patternallocated to each unit section of the track groove, the contents of thesubdivided information allocated to the unit section can be read.Accordingly, various types of information can be read based on multi-bitsubdivided information.

As described above, the difference in waveform between the wobblepatterns is represented as a difference in gradient between the leadingedges or the trailing edges of the read signals as obtained by thedifferential push-pull detection. Accordingly, the wobble pattern of theunit section 22, for example, is easily identifiable as one of thewobble patterns 105 and 106 shown in FIG. 2A. However, when thisdetection is performed by differentiating the read signal in theabove-described manner, noise components increase. For that reason, ifthis technique is applied to a high-density optical disk medium thatresults in a low SN ratio, then detection errors may occur. To avoid theoccurrence of such detection errors, the following technique is adoptedin this embodiment.

The information to be written by the user on the disk (which will beherein referred to as “recording information”) is written over severalblocks along the track groove on the recording layer. The recordinginformation is written on a block-by-block basis. Each block extendsfrom the block mark 210 along the track groove 2 and has a predeterminedlength of e.g., 64 kilobytes. A block like this is a unit of informationprocessing and may mean an ECC block, for example. Each block is made upof a number N (which is a natural number) of sub-blocks. When each blockhas a length of 62 kilobytes and each sub-block has a length of 2kilobytes, the number N of sub-blocks included in one block is 32.

In this embodiment, the areas on the track groove where the informationfor respective sub-blocks should be written correspond to the unitsections 22, 23 of the track groove.

Since one-bit subdivided information “0” or “1” is recorded on each ofthe unit sections 22 and 23, a group of subdivided information of N=32bits is allocated to each block. In this embodiment, the address of theblock is indicated by this group of subdivided information of 32 bits.

For example, where each unit section has a length of 2,418 bytes (=2,048bytes plus parity) and one wobble period has a length corresponding to11.625 bytes, a wobble pattern for 208 periods is included in each unitsection. Accordingly, the wobble signal 206 shown in FIGS. 3B and 3C maybe detected over 208 wobble periods (i.e., a wave number of 208) toidentify the type of the given wobble pattern. For that reason, even ifsome detection errors have been caused by noise during signal reading,the subdivided information is identifiable accurately enough.

More specifically, the differentiated waveform of the differentialpush-pull signal (i.e., the pulse signal 208) may be sampled and heldevery time the signal rises or falls. And if the accumulated value ofthe number of rises is compared to that of the number of falls, then thenoise components are canceled. As a result, the subdivided informationcomponents can be extracted highly accurately.

The block mark 210 shown in FIG. 4 is formed by discontinuing the trackgroove 2 for just a short length. Accordingly, if information isoverwritten on that part of the recording layer over the block mark 210,then some problems may arise. Specifically, since the quantity of lightreflected greatly changes depending on whether or not the groove ispresent at the spot, the existence of the block mark 210 causes adisturbance in the read signal. Thus, in this embodiment, a VFO(variable frequency oscillator) recording area 21 is allocated to anarea 21 of a predetermined length including the block mark 210. The VFOrecording area 21 is an area where a single frequency signal VFO iswritten. VFO is a signal for locking a PLL required for reading therecorded information. Even when there is any disturbance or variation,the VFO signal would cause a jitter just locally but no errors. Also,the VFO signal has a single repetitive frequency. Accordingly, it ispossible to separate the disturbance caused by the block mark. However,the signal to be written on the VFO recording area 21 does not have tohave a single frequency, but may have a particular pattern and aspectral bandwidth narrow enough to separate the frequency thereof fromthat of a signal corresponding to the block mark 210.

Embodiment 2

Hereinafter, an optical disk apparatus (disk drive) having the functionof reading an address on the optical disk medium of the first embodimentwill be described with reference to FIG. 5.

A laser beam, emitted from the optical head 331 of this apparatus,impinges onto an optical disk 1, thereby forming a light spot on thetrack groove of the optical disk 1. A drive mechanism is controlled insuch a manner that the light spot moves on the track groove as theoptical disk 1 is rotated.

The optical head 331 then receives the laser beam that has beenreflected by the optical disk 1, thereby generating an electric signal.The electric signal is output from the optical head 331 and then inputto a read signal processor 332 where the electric signal is subjected tooperation processing. In response to the signal supplied from theoptical head 331, the read signal processor 332 generates and outputs afully added signal and a wobble signal (i.e., push-pull signal).

The wobble signal is input to a wobble PLL circuit 333. The wobble PLLcircuit 333 generates a clock signal from the wobble signal and thendelivers the clock signal to a timing generator 335. The clock signalhas a frequency obtained by multiplying the wobble frequency. It shouldbe noted that before the wobble PLL section 333 is phase-locked, atiming signal may also be generated by using a reference clock signalalthough the precision is inferior.

The fully added signal, output from the read signal processor 332, isinput to a block mark detector 334. In accordance with the fully addedsignal, the block mark detector 334 locates the block mark 210. In theoptical disk of the first embodiment, the laser beam, reflected from apart where the block mark 210 is present, has a higher intensity thanthe other parts. Accordingly, when the level of the fully added signalexceeds a predetermined level, the read signal processor 332 generates ablock mark detection signal and sends it out to the timing generator335.

In response to the block mark detection signal and the clock signal, thetiming generator 335 counts the number of clock pulses from thebeginning of a block. By performing this counting, it is possible todetermine the timing at which the wobble signal should rise or fall, thetiming at which the information is subdivided and the timing at whicheach block is sectioned.

A first shape counter 336 counts the number of times the gradient of thewobble signal rising is equal to or greater than a predetermined valueU_(TH) for each unit section. More specifically, if the gradient of thepush-pull signal is equal to or greater than the predetermined valueU_(TH) when the wobble signal rises, the counter 336 increments itscount C1 by one. On the other hand, if the gradient is less than U_(TH),then the counter 336 does not change its count C1 but holds it. Thetiming at which the wobble signal rises is defined by the output signalof the timing generator 335.

A second shape counter 337 counts the number of times the gradient ofthe wobble signal falling is equal to or smaller than a predeterminedvalue D_(th) for each unit section. More specifically, if the gradientof the push-pull signal is equal to or smaller than the predeterminedvalue D_(TH) when the wobble signal falls, the counter 337 incrementsits count C2 by one. On the other hand, if the gradient is greater thanD_(TH), then the counter 337 does not change its count C2 but holds it.The timing at which the wobble signal falls is also defined by theoutput signal of the timing generator 335.

A subdivided information detector 338 compares the count C1 of the firstshape counter 336 with the count C2 of the second shape counter 337 inresponse to the timing signal that has been generated by the timinggenerator 335 to indicate the timing at which the information should besubdivided. If C1≧C2 is satisfied for a certain unit section, then thedetector 338 outputs “1” as the subdivided information of the unitsection. On the other hand, if C1<C2 is satisfied for a unit section,then the detector 338 outputs “0” as the subdivided information of theunit section. In other words, the detector 338 decides the type of thewobble signal by majority on a unit section basis.

An error corrector 339 makes an error correction on the group ofsubdivided information allocated to a plurality of unit sectionsincluded in one block, thereby obtaining address information.

These circuits do not have to be separately implemented as mutuallyindependent circuits. Alternatively, a single circuit component may beshared by a plurality of circuits. Also, the functions of these circuitsmay be executed by a digital signal processor whose operation iscontrolled in accordance with a program pre-stored on a memory. The samestatement will also be true of each of the following various embodimentsof the present invention.

Embodiment 3

Another embodiment of the optical disk apparatus of the presentinvention will be described with reference to FIG. 6. The optical diskapparatus of this embodiment is different from the apparatus accordingto the fourth embodiment in that the apparatus further includes anerasure detector 340. The error corrector 339 also has a differentfunction. In the other respects, the apparatus of this embodiment is thesame as the counterpart of the second embodiment. Thus, the descriptionof the components commonly used for these two embodiments will beomitted herein.

The erasure detector 340 compares the count C1 output from the firstshape counter 336 with the count C2 output from the second shape counter337 for each unit section. And when an inequality −E<C1−C2<+E issatisfied with respect to a predetermined value E, the detector 340outputs an erasure flag of “1” indicating that the subdividedinformation is not definitely identifiable. On the other hand, if theinequality −E<C1−C2<+E is not satisfied, the detector 340 outputs anerasure flag of “0”.

If the erasure flag is “1”, the error corrector 339 erases thesubdivided information, thereby making an error correction compulsorily.

In this embodiment, error bits are erased using the erasure flags inthis manner. Thus, the number of error-correctible bits of an errorcorrection code is doubled.

It should be noted that as the erasure flag, “0” may be output whenC1−C2≦−E, “X” may be output when −E<C1−C2<+E and “1” may be output when+E≦C1−C2. In that case, if the erasure flag is “X”, the error correctionmay be made compulsorily.

As described above, in the optical disk reproducing apparatus of thisembodiment, if subdivided information is not definitely identifiable dueto a small difference between the first and second shape counts, thenbits in question are erased during an error correction process. In thismanner, the error correction ability is improved and an address can beread more reliably.

Embodiment 4

An inventive method for reading an address on an optical disk mediumwill be described with reference to FIG. 7.

A wobble shape 351 is schematically illustrated on the upper part ofFIG. 7. In the left half of the wobble shape 351, falling displacementsare steep. In the right half thereof on the other hand, risingdisplacements are steep.

The wobble signal 352 as represented by a push-pull signal has had itsquality deteriorated by noise or waveform distortion.

A digitized signal 353 is obtained by slicing the wobble signal 352 atzero level. A differentiated signal 354 is obtained by differentiatingthe wobble signal 352. The differentiated signal 354 containsinformation about the gradients of the wobble shape. A number of peaksreflecting noise or waveform distortion are observed here and there inaddition to those peaks representing the gradients detected fordisplacement points.

For the sake of simplicity, only first and second parts 355 and 356 thatare arbitrarily selected from the wobble signal will be described.

In the first part 355 of the wobble signal, when the values 357 and 358of the differentiated signal 354 that are sampled with respect toleading and trailing edges of the digitized signal 803, respectively,have their absolute values compared with each other, the sampled value358 has the greater absolute value. Accordingly, it may be decided thatthe wobble signal including the first part 355 has a wobble pattern inwhich a falling displacement is steeper than a rising displacement.

In the same way, as for the second part 356 of the wobble signal, whenthe values 359 and 360 of the differentiated signal 354 that are sampledwith respect to leading and trailing edges of the digitized signal 803,respectively, have their absolute values compared with each other, thesampled value 359 has the greater absolute value. Accordingly, it may bedecided that the wobble signal including the second part 356 has awobble pattern in which a rising displacement is steeper than a fallingdisplacement.

By making such a decision on a wobble period basis and by accumulatingthe decisions, the type of each subdivided information unit isidentifiable by majority.

In this manner, according to the address reading method of the presentinvention, the differentiated signal is sampled only at the timingscorresponding to the edges of the signal obtained by digitizing thewobble signal, and the sampled values are compared with each other. As aresult, the gradients of the wobble shape at the displacement points aredetectable highly reliably even under some disturbance such as noise orwaveform distortion.

Embodiment 5

Another optical disk reproducing apparatus for reading an address on anoptical disk according to the present invention will be described withreference to FIG. 8.

The reproducing apparatus of this embodiment is different from thecounterpart shown in FIG. 5 in that the drive of this embodimentincludes a wobble shape detector 361. The wobble shape detector 361identifies a given wobble shape as a first shape with a steep risingdisplacement or as a second shape with a steep falling displacement on awobble period basis, thereby outputting wobble shape information to thesubdivided information detector 338. In accordance with the wobble shapeinformation obtained from the wobble shape detector 361, the subdividedinformation detector 338 determines which shape has been detected thegreater number of times, the first shape or the second shape. Then, thedetector 338 identifies and outputs the subdivided information allocatedto a given subdivided information unit.

The subdivided information detector 338 may include: a counter forobtaining the number of times that a signal indicating the detection ofthe first shape has been received in accordance with the wobble shapeinformation received; and another counter for obtaining the number oftimes that a signal indicating the detection of the second shape hasbeen received in accordance with that information. By comparing thecounts of these two shapes with each other, a decision by majority maybe made. Alternatively, an up/down counter may also be used to incrementthe count by one when the first shape is detected and to decrement thecount by one when the second shape is detected. In that case, thesubdivided information may be represented by the sign of the count ofthe up/down counter, i.e., seeing whether the count of the up/downcounter is positive or negative, at the end of a given unit section.

Next, it will be described in detail with reference to FIG. 9 how thewobble shape detector 361 operates.

The wobble shape detector 361 includes a band-pass filter (BPF) 362,which receives the push-pull signal (i.e., the wobble signal) andreduces unwanted noise components thereof. This BPF 362 may pass thefundamental frequency components of the wobble signal and harmonicfrequency components including wobble gradient information. Supposingthe wobble signal has a fundamental frequency of fw, a band-pass filterhaving a band ranging from ½ fw to 5 fw is preferably used to allow agood margin for possible variation in linear velocity.

The output of the BPF 362 is input to a gradient detector 363 and adigitizer 365.

The gradient detector 363 detects the gradient of the wobble signal.This “gradient” detection may be carried out by differentiating thewobble signal. Instead of the differentiator, a high-pass filter (HPF)for extracting only harmonic components including gradient informationmay also be used. The output of the gradient detector 363 is deliveredto a rise detector 366 and an inverter 364.

The inverter 904 inverts the output of the gradient detector 363 withrespect to the zero level and then outputs the inverted value to a fallvalue acquirer 367.

The digitizer 905 detects rising and falling zero-cross timings of thewobble signal. The “rising zero-cross timing” herein means a time atwhich the wobble signal changes from “L” level into “H” level. On theother hand, the “falling zero-cross timing” herein means a time at whichthe wobble signal changes from “H” level into “L” level.

The rise value acquirer 366 samples and holds the gradient of the wobblesignal, i.e., the output of the gradient detector 363, at the risingzero-cross timing that has been detected by the digitizer 365. In thesame way, the fall value acquirer 367 samples and holds the invertedgradient of the wobble signal, i.e., the output of the inverter 364, atthe falling zero-cross timing that has been detected by the digitizer366.

In this case, the value sampled by the rise value acquirer 366 is apositive value because this value represents the gradient of a risingedge. The value sampled by the fall value acquirer 367 is also apositive value because this value represents the inverted gradient of afalling edge. That is to say, the values sampled by the rise and fallvalue acquirers 366 and 367 correspond to the absolute values of therespective gradients.

A comparator 369 compares the absolute value of the rising edge gradientas sampled and held by the rise value acquirer 366 to the absolute valueof the falling edge gradient as sampled and held by the fall valueacquirer 377 after a predetermined time has passed since the fallingzero-cross timing of the wobble signal. This predetermined amount oftime delay is caused by a delay circuit 368. If the value of the risevalue detector 366 is found the greater, the comparator 369 outputswobble shape information indicating the first shape. Otherwise, thecomparator 369 outputs wobble shape information indicating the secondshape. That is to say, by comparing only the gradients at the rising andfalling zero-cross timings, at which the wobble signal gradientinformation is most reliable (i.e., the differentiated values thereofwill be the maximum and minimum, respectively), to each other, thewobble shape is detectable accurately enough.

In this embodiment, the same signal is input to both the digitizer 365and the gradient detector 363. However, the present invention is notlimited to this particular embodiment. To detect the zero-cross timingsof the wobble signal even more accurately, the output of the BPF 362 maybe input to the digitizer 365 by way of a low-pass filter (LPF). Also,the BPF 362 may be replaced with two types of BPFs with mutuallydifferent characteristics that are provided for the gradient detector363 and the digitizer 365, respectively. In that case, to match thephases of the wobble signal that has been passed through these BPFs, adelay corrector is preferably further provided separately.

As described above, in the optical disk reproducing apparatus of thisembodiment, the gradients of a wobble signal including subdividedinformation are sampled and held at zero-cross timings of the wobblesignal and then the values held are compared to each other. In thismanner, the wobble shape is identifiable accurately enough and detectionerrors of subdivided information as caused by noise, for example, arereducible.

Embodiment 6

FIG. 10 illustrates a configuration in which a block mark 210 is placedapproximately at the center of a VFO recording area 21. In the exampleillustrated in FIG. 10, a wobble having a rectangular waveform has beenformed in the VFO recording area 21. However, the present invention isnot limited to this particular embodiment.

Hereinafter, it will be described with reference to FIGS. 11A and 11Bhow to write a signal on the VFO recording area 21. In FIGS. 11A and11B, the wobble formed on the track groove 2 is omitted for the sake ofsimplicity.

FIG. 11A illustrates a situation where a signal corresponding to oneblock is written on the track groove 2. A recording signal for one blockincludes data (DATA) 202 and VFOs 201 and 203.

Writing on each block begins with the VFO 201. In this embodiment, theVFO 202 is written within the VFO area 21 and the writing start point ofthe VFO 202 is ahead of the block mark 210. After the VFO 202 has beenwritten, the DATA 202 for one block is written and then the VFO 203 iswritten finally. The VFO 203 is written within the VFO area 31 and thewriting end point of the VFO 203 is behind the block mark 210. That isto say, in this embodiment, information starts to be recorded before theblock mark located at the beginning of an intended recording area isreached, and then finishes being recorded after the block mark locatedat the end of the intended recording area has been passed.

If data starts to be written at the center of the block mark 210, thenthe recording film deteriorates considerably at its part where the blockmark 210 is present. The block mark 210 of this embodiment is formed bydiscontinuing the track groove 2 for just a short length. Accordingly,steps have been formed on the track groove where the block mark 210 ispresent. In recording information on those stepped parts, theinformation needs to be recorded on the recording film by irradiatingparts of the recording film with a high-energy laser beam so that theirradiated parts will be given a high thermal energy. In this case,steep temperature gradients are formed before and after those partsirradiated with the laser beam. These temperature gradients produce astress in the recording film. If any of the steps exists in the stressedpart, then a small crack might be formed in the recording film. Oncethat small crack has been formed in the recording film, the crack willexpand every time the write operation is repeatedly carried out. Then,the film might be broken in the end.

In this embodiment, to prevent such film breakage, the writing start andend points are placed in the areas where no block marks 211 are present.

The VFO is a dummy signal for preparing for data reading. While the VFOsignal is being read, the slice level of the data is feedback-controlledat the center of the read signal and the PLL is locked to extract aclock signal. To read data with high fidelity, the read data signalneeds to be digitized and clocked accurately enough. If a VFO signalinterval is too short, then the data starts to be read before the PLLhas been locked sufficiently, thus possibly causing errors in the dataread out from the beginning of a block. Accordingly, the VFO preferablystarts to be written ahead of the block mark and is preferably providedwith a sufficiently long area.

It should be noted that if data has already been written on the previousblock, then a VFO for the current block to be written might beoverwritten on a VFO for the previous block as shown in FIG. 11B. Inthat case, part of the VFO signal already written is erased. Also, thepreexistent VFO may not be in phase with the overwritten VFO.Accordingly, it is not preferable to get the PLL for the current blocklocked by using the VFO of the previous block.

The foregoing description of this embodiment relates to the VFO writingstart point. Similar recording film deterioration is also observedaround the data writing end point. However, the writing end point ispreferably behind the block mark 310, not before. If the writing endpoint was located ahead of the block mark 310, then a gap might beformed between the current block and the following block. This gap is anarea that is not irradiated with the high-power light and in which nomarks are formed. Just like the steps, such a gap might contribute tothe film deterioration. Accordingly, the VFO at the end of thepreviously written block preferably overlaps with the VFO at thebeginning of the current block to be written. This VFO overlap isachieved by setting the VFO writing start point ahead of the block mark210 and the VFO writing end point behind the block mark 310,respectively, as shown in FIG. 11A.

The distance between the block mark and the VFO writing start or endpoint is preferably about 10 or more times as long as the beam spot sizeof the laser light for writing. A beam spot size is obtained by dividingthe wavelength of laser light by an NA value. Accordingly, when anoptical head, which emits laser light having a wavelength of 650 nm andhas an NA of 0.65, is used, the size of a beam spot formed on a disk is1 μm (=wavelength/NA). In that case, the writing start or end point ispreferably 10 μm or more distant from the block mark. However, thatreference distance obtained by multiplying the beam spot size by ten maybe correctible depending on the properties (e.g., thermal conductivity,in particular) of the recording film.

It should be noted, however, that when the write operation is startedahead of the block mark 210, the block mark has not been detected yet.Accordingly, to start writing exactly before the block mark, thelocation of the block mark should be predicted or estimated in some wayor other. For example, after the block mark of the previous block hasbeen detected, the number of clock pulses of the clock signal may becounted. And when the count reaches a predetermined number, the VFO maystart to be written on the next block.

Embodiment 7

An optical disk medium according to a seventh embodiment will bedescribed with reference to FIG. 12. In the embodiment described above,the block mark 210 is placed approximately at the center of the VFOrecording area 21. In contrast, according to this embodiment, a blockmark 211 is formed closer to the previous block with respect to thecenter of the VFO recording area 21 as shown in FIG. 12. In such aconfiguration, the VFO may be longer at the beginning.

Embodiment 8

An optical disk medium according to an eighth embodiment will bedescribed with reference to FIGS. 13, 14A and 14B.

The block mark 210 of this embodiment is made up of sub-marks 210 a and210 b. According to this configuration, the write operation can be timedmore easily. That is to say, since two marks have been formed, the writeoperation may be started after the mark 210 b at the beginning of ablock has been detected and before the mark 210 a is detected. Also, thewrite operation may be ended after the second mark 210 a located at thebeginning of the next block has been detected.

In this manner, the writing start point can be set accurately enoughwithout counting the number of clock pulses after the block mark of theprevious block has been detected.

It should be noted that to avoid the film deterioration, the spacebetween these marks 210 a and 210 b should be sufficiently wide.Specifically, to set the distance between the writing start point andthe mark 210 a or 210 b about 10 or more times as long as the beam spotsize, the space between the marks 210 a and 210 b should preferably beabout 20 or more times as long as the beam spot size. For example, wherethe size of a beam spot formed on an optical disk is 1 μm, this space ispreferably set to 20 μm or more.

Embodiment 9

An optical disk according to a ninth embodiment will be described withreference to FIG. 15. In each of the embodiments described above, theblock mark 210 is formed by discontinuing the track groove 2 for just ashort length. In such a part where the track groove is discontinued, nogroove exists. Accordingly, that part is flat and is called a “mirrormark”. A mirror mark reflects read light at a high reflectance and iseasily detectable. In this embodiment, however, the block mark is notformed as a mirror mark but a block mark 218 in a different shape isadopted. Hereinafter, this block mark 218 will be described in detail.

In this embodiment, the wobble phase of the track groove is invertedinside the VFO recording area 21 and this part with the inverted phaseis used as the block mark 218 as shown in FIG. 15.

As described above, the block mark 210 as a mirror mark advantageouslyensures high positioning accuracy and is easily detectable. However, ifthe SN ratio is low, then detection errors increase considerably. Incontrast, if the track groove is formed in such a manner that the wobblephase before the block mark 218 is the inverse of the wobble phase afterthe block mark 218, the passage of the block mark 218 may be sensed atany time by observing the wobble phase after the block mark 218 has beenpassed. This passage is sensible even if the wobble phase change point(i.e., the block mark 218) could not be located due to noise, forexample.

Embodiment 10

Another embodiment of the inventive optical disk will be described withreference to FIG. 16. In this embodiment, two block marks 218 a and 218b are provided inside each VFO recording area 21. Each of these blockmarks 218 a and 218 b is formed by inverting the wobble phase of thetrack groove.

The main difference between this embodiment and the embodimentillustrated in FIG. 15 is whether the number of times the wobble phaseis inverted between a pair of blocks is an odd number or an even number.As shown in FIG. 15, where the wobble phase is inverted just once (i.e.,an odd number of times) within each VFO recording area 21, the wobblephase will be kept inverted to that of the previous block since thephase has been inverted and until the next block mark is passed. As aresult, if a clock signal is extracted as it is from the wobble of thetrack groove by a PLL synchronization technique, then the output of thephase comparator of the PLL will have its polarity inverted and the PLLwill slip disadvantageously. For that reason, if the wobble phase isinverted an odd number of times as in the example illustrated in FIG.15, the polarity of the PLL needs to be inverted after the block markhas been passed.

In contrast, according to this embodiment, the phase that has been onceinverted (at the block mark 218 a) is inverted again (at the block mark218 b). Thus, the wobble phase becomes the same as that of the previousblock. Accordingly, there is no need to invert the polarity of the PLL.

In each VFO recording area 21, the interval between the block marks 218a and 218 b needs to be longer than expected defect noise. However, ifthis interval is longer than the response time of the PLL, theprobability of occurrence of the slip increases. In view of theseconsiderations, the interval between the block marks 218 a and 218 bwithin each VFO recording area 21 is preferably about three to about tentimes as long as the wobble frequency.

It should be noted that the number of the block marks 218 a, 218 binside each VFO recording area 21 is not limited to two but may beanother even number to achieve effects similar to those of thisembodiment. However, more than four block marks 218 a, 218 b should notbe formed within a limited length in view of the density of integration.

In the fourth and fifth embodiments described above, the block marks areformed by inverting the wobble phase. However, so long as the phasechange is detectable, the phases before and after the block mark do nothave to be shifted from each other by 90 degrees precise. The shift inwobble phase at the block mark is preferably from 45 degrees to 135degrees, for example.

Embodiment 11

Next, a sixth embodiment of the present invention will be described withreference to FIG. 17.

This embodiment is different from the foregoing embodiments in theconfiguration of the block mark 219. Specifically, the block mark 219 ofthis embodiment is defined by a wobble having a frequency different fromthe wobble frequency of the groove located inside the block. In theillustrated example, the wobble frequency of the block mark 219 ishigher than that inside the block. Accordingly, if part of a readsignal, which has a locally different wobble frequency, is separated oridentified by processing the read signal using a band pass filter, forexample, then the block mark 219 can be located highly accurately.

In the optical disk medium of this embodiment, the block mark 219 isalso formed inside the VFO recording area 21, and VFO data is alsowritten on the area where the block mark 219 is present.

The wobble frequency of the block mark 219 is preferably set 1.2 to 3.0times as high as, more preferably 1.5 to 2.0 times as high as, thewobble frequency inside the block. If the wobble frequency of the blockmark 219 is too close to that inside the block, then it is hard todetect the block mark 219. On the other hand, if the wobble frequency ofthe block mark 219 is too much higher than that inside the block, thenthe former wobble frequency will get closer to the signal frequency ofthe information to be written on the recording film. As a result, thesesignals will interfere with other disadvantageously.

It should be noted that in the space between a pair of blocks, a wobblehaving the same frequency as the wobble frequency inside the blocks ispreferably formed except the area of the block mark 219. In theblock-to-block space, the wobble shape is preferably different from thewobble shape inside the blocks. In the example illustrated in FIG. 17,the block-to-block groove wobbles in a sine wave curve.

Embodiment 12

Next, a seventh embodiment of the present invention will be describedwith reference to FIG. 18.

In this embodiment, no shape that has its amplitude, frequency or phasechanged locally is used as the block mark, but a groove itself wobblingin a sine waveform curve is used as the block mark. Also, the beginningof each sub-block 221 or 222 includes a wobble 228 or 229 with a locallychanged frequency.

By placing such an area having a wobble frequency different from thefundamental wobble frequency at the beginning of each sub-block in thismanner, the boundary between the sub-blocks is detectable correctly. Inthe foregoing embodiments, a sub-block is located by counting the numberof wobbles from the block mark. On the other hand, in this embodiment, asub-block can be located by counting the number of sub-block marks 228,2229 provided for the respective sub-blocks.

It should be noted that a block mark similar to the counterpart of anyof the foregoing embodiments may be formed at an appropriate positioninside the VFO area 21. Also, in this embodiment, the sub-blockidentification mark 228, 229 having a locally different wobble frequencyis formed at the beginning of each sub-block 221, 222. Alternatively,the sub-block mark 228, 229 may be placed at the end of each sub-block.Also, the identification marks 228, 229 do not have to be provided forall sub-blocks but may be provided for only odd-numbered oreven-numbered sub-blocks.

Because of the same reasons as those described above, the wobblefrequency of the sub-block marks 228, 229 is preferably 1.2 to 3.0 timesas high as, more preferably 1.5 to 2.0 times as high as, that of theother parts.

The sub-block marks 228, 229 are preferably used for indicating thebeginning thereof but may represent any other type of information. Forexample, the address of a block or any other associated block may berecorded by using a plurality of sub-block marks included in the formerblock. Or any other type of information may be recorded by using thesub-block marks. When the address of a block is recorded by using aplurality of sub-block marks, the address is also recorded by thewobbles inside the block. Thus, the address obtained is much morereliable.

In recording multi-bit information as a combination of these sub-blockmarks, the sub-block marks should have mutually different andidentifiable shapes corresponding to two or more values. For thispurpose, the wobbles of those sub-block marks may be given mutuallydifferent frequencies or may be subjected to mutually different types ofphase modulation.

Next, a circuit configuration for generating a clock signal and readingaddress information from an optical disk medium according to thisembodiment will be described with reference to FIG. 19.

First, a photodetector 901 that has been divided in a direction verticalto the tracking direction (i.e., in the disk radial direction) and adifferential amplifier 371 are used to generate an electric signalincluding signal components corresponding to the wobble of the groove.Next, a low-pass filter (LPF) 374 extracts only the fundamental periodcomponents of a wobble signal from this read signal. The signal havingonly the fundamental period components is supplied to a clock generator373. The clock generator 373 may be implemented as a PLL circuit, forexample, and multiplies the fundamental period signal received by apredetermined number, thereby generating a clock signal for use inread/write signal synchronization processing.

On the other hand, a high-pass filter (HPF) 375 selectively passes theharmonic components included in the read wobble signal. The output ofthe high-pass filter 375 includes: high frequency componentscorresponding to the sub-block marks 228 and 229 shown in FIG. 18; andsteep edge components of a saw-tooth signal generated by a saw-toothwobble.

A sub-block mark detector 377 detects the wobble components having apredetermined frequency and corresponding to the sub-block marks 228 and229. On detecting these marks, the detector 377 generates a timingsignal. The timing signal output from the sub-block mark detector 377 issent to an address decoder 378.

As described above, a steep edge of a saw-tooth wobble has its polarityinverted depending on whether it represents “1” or “0” of addressinformation. In accordance with the output of the high-pass filter 375,an address information detector 376 detects this polarity inversion andsends out a bit stream to the address decoder 378. On receiving this bitstream, the address decoder 378 decodes the address information inresponse to the timing signal that has been output from the sub-blockmark detector 377.

In this embodiment, an identification mark, on which a VFO signal can beoverwritten, is formed for each block and an address is represented bythe wobble of the groove. As a result, an optical disk medium, on whichinformation is stored on a block-by-block basis and which is suitablyapplicable to high-density recording, is provided. Also, by starting orending the write operation at a position sufficiently distant from thisidentification mark, the deterioration of the recording film isreducible.

Embodiment 13

Next, FIG. 20 will be referred to.

On an optical disk according to this embodiment, address information 301is recorded as the high-order 21 bits of a group of subdividedinformation of 32 bits. Parity bits 302 used as an error correction codeare recorded as the intermediate 10 bits of the 32-bit subdividedinformation group. And additional information 303 is recorded as theleast significant bit. If this optical disk has two recording layers,then “0” may be recorded as the additional information 303 for the firstrecording layer and “1” may be recorded as the additional information303 for the second recording layer. However, the contents of theadditional information 303 are not limited to such layer information.Alternatively, the amount of information represented by the additionalinformation 303 may be increased by combining multiple pieces ofadditional information of a series of blocks. Then, information evenmore complicated than the layer information, e.g., copyright informationor manufacturer information, is can be stored. A simple parity bit as anexclusive logical sum of the 21-bit address information or the 31-biterror correction code may also be used. In that case, the ability oferror detection or error correction is improvable. Also, everyadditional information may be “1”. Furthermore, if only a block markthat follows a unit section with subdivided information of “1” isidentified as the block mark, then the block mark detection accuracy isimprovable.

In this embodiment, the 31-bit error correction code is a BCH code,which is well known as a code for correcting 2 or more error bits.Supposing the 31-bit address information is represented by b0, b1, . . ., b20 and the 10 parity bits are represented by p0, p1, . . . , p9 asshown in FIG. 20, an information polynomial I(x) is given by Equation(1) and a parity polynomial P(x) is given by Equation (2), P(x) isgenerated by Equation (3). In that case, the generator polynomial G(x)is given by Equation (4). This is well known as a (31, 21) BCH code, inwhich arbitrary 2 bits included in a 31-bit codeword may beerror-corrected. $\begin{matrix}{{I(x)} = {\sum\limits_{i = 0}^{20}{b_{i} \cdot x^{i}}}} & \text{(Equation~~1)} \\{{P(x)} = {\sum\limits_{i = 0}^{9}{p_{i} \cdot x^{i}}}} & \text{(Equation~~2)}\end{matrix}$

 P(x)=x ¹⁰ ·I(x)mod G(x)  (Equation 3)

G(x)=x ¹⁰ +x ⁹ +x ⁸ +x ⁶ +x ⁵ +x ³+1  (Equation 4)

On the optical disk of this embodiment, the address information, paritybits and additional information are arranged in this order. However, thepresent invention is not limited thereto. So long as the arrangement isfixed in advance, no matter where the group of subdivided information,including the 21-bit address information, 10 parity bits and 1-bitadditional information, is placed, these bits may be processed byrearranging them to their original positions. On the optical disk ofthis embodiment, each block has 32-bit subdivided information.Alternatively, even when each block has subdivided information of 26bits, 52 bits, 64 bits, etc., similar effects are achievable byselecting an appropriate error correction code.

As described above, in the optical disk medium of this embodiment, oneinformation block is subdivided into a number N (=32) of sub-blocks. Andby pre-forming a wobble in such a shape as representing each piece ofsubdivided information for each section corresponding to each sub-block,an address can be formed without any overhead or without providing anypre-pits between adjacent parts of the groove. Furthermore, the wobblesformed in this embodiment have a constant wobble frequency even thoughthe rising or falling edges thereof may have different shapes amongrespective pieces of subdivided information. Accordingly, in extractinga write clock signal from the wobble signal, after noise components havebeen removed therefrom using a band-pass filter that has a bandwidthbroad enough to pass its frequency, the signal may be simply multipliedand synchronized using a PLL. Then, a clock signal with a reduced jittercan be obtained. Furthermore, by classifying the subdivided informationgroup into the address information part and the parity part and by usingthis subdivided information group as an error correction code, addressinformation is readable highly reliably.

Embodiment 14

FIG. 21 illustrates a bit allocation for a subdivided information groupon an optical disk medium according to a fourteenth embodiment. Itshould be noted that although the subdivided information group of theoptical disk of this embodiment has a format different from that of theoptical disk of the thirteenth embodiment, the optical disk of thisembodiment has the same subdivided information arrangement or shapes asthe optical disk of the thirteenth embodiment.

Address information is normally arranged sequentially. Accordingly, ifthe address of the preceding block is known, then the address of theblock succeeding the former block is predictable. However, when anerroneous track jump happens, for example, continuity cannot be keptanymore. Nevertheless, the address discontinuity caused by the erroneoustrack jump or the like is often observed only in low-order bits. Also,the high-order bits are estimable from the radial position of theoptical head, for example. Thus, the low-order bits of addressinformation may be regarded as the more variable and the more important.

In view of these considerations, on the optical disk of this embodiment,the 21-bit address information is divided into high-order addressinformation 311 of 14 bits and low-order address information 312 of 7bits. One high-order parity bit 313 is added to the high-order addressinformation 311 to make an error correction code (or error detectioncode) of 15 bits. Furthermore, eight low-order parity bits 314 are addedto the low-order address information 312 to make another errorcorrection code of 15 bits. And 2-bit additional information 315 isfurther added, thereby forming a subdivided information group of 32bits. It should be noted that the additional information 315 is almostthe same as the additional information 303 of the thirteenth embodiment.

In this embodiment, the 15-bit error correction code, made up of thelow-order address information 312 and the low-order parity bits 314, isa BCH code, which is well known as a code for correcting 2 or more errorbits. Supposing the 7-bit low-order address information 312 isrepresented by b0, b1, . . . , b6 and the eight low-order parity bits314 are represented by p0, p1, . . . , p7, an information polynomialI(x) is given by Equation (5) and a parity polynomial P(x) is given byEquation (6), P(x) is generated by Equation (7). In that case, thegenerator polynomial G(x) is given by Equation (8). This is well knownas a (15, 7) BCH code, in which arbitrary 2 bits included in a 15-bitcodeword may be error-corrected. $\begin{matrix}{{{I(x)} = {\sum\limits_{i = 0}^{6}b_{i}}}{\cdot x^{i}}} & \text{(Equation~~5)} \\{{P(x)} = {\sum\limits_{i = 0}^{7}{p_{i} \cdot x^{i}}}} & \text{(Equation~~6)}\end{matrix}$

 P(x)=x ⁸ ·I(x)mod G(x)  (Equation 7)

 G(x)=x ⁸ +x ⁷ +x ⁶ +x ⁴+1  (Equation 8)

Also, supposing the 14-bit high-order address information 311 isrepresented by b8, b9, . . . , b20, the high-order parity bit 313 (whichis herein represented by p10) is an even parity bit given by p10=b8+b9+. . . b20 (where “+” is an exclusive-OR operator). In this case,arbitrary one error bit included in a codeword may be detected. In thismanner, by using a parity bit with a small redundancy for the high-orderaddress information and parity bits with a large redundancy for thelow-order address information, respectively, the low-order bits of theaddress information can have “more heavily weighted ” error correctionability so to speak.

For the optical disk of this embodiment, two error correction codes areobtained by adding one parity bit to the high-order 14 bits of theaddress information and eight parity bits to the low-order 7 bits of theaddress information, respectively. However, the numbers of the high- andlow-order bits divided are not limited thereto. For example, one paritybit may be added to high-order 16 bits and 10 parity bits may be addedto the low-order 5 bits (where the low-order bits are part of a (15, 5)BCH code). Also, no parity bits may be added to high-order 9 bits and 11parity bits may be added to the low-order 12 bits (where the low-orderbits are part of a (23, 12) BCH code).

As described above, the optical disk medium of this embodiment alsoachieves the effects of the optical disk medium of the thirteenthembodiment. In addition, in this embodiment, the address information isdivided into high- and low-order bits and the low-order bits areprovided with higher error correction ability, thereby reading theaddress information even more reliably.

However, the optical disk media of the thirteenth and fourteenthembodiments each use a BCH code, which is a complicated error correctioncode. Thus, these media have a problem in that a circuit required forreading addresses therefrom should have a large size.

Embodiment 15

FIG. 22 illustrates a bit allocation for a subdivided information groupon an optical disk medium according to a fifteenth embodiment. It shouldbe noted that although the subdivided information group of the opticaldisk medium of this embodiment has a format different from that of theoptical disk medium of the thirteenth embodiment, the optical diskmedium of this embodiment has the same subdivided informationarrangement or shapes as the optical disk of the thirteenth embodiment.As shown in FIG. 22, the subdivided information group on the opticaldisk medium of this embodiment is made up of 21-bit address information321 and 11 parity bits 322, i.e., 32 bits in total.

Hereinafter, a more detailed arrangement will be described withreference to FIG. 23. The 21 bits b0 through b20 of the addressinformation 321 are arranged in 7 rows and 3 columns so that the threerows include b20 through b14, b13 through b7 and b6 through b0,respectively. Each row made up of 7 bits is provided with one additionalparity bit to make 8 bits in total, while each column made up of 3 bitsis also provided with one additional parity bit to make 4 bits in total.In this manner, an error correction code of 32 bits (=(7+1)×(3+1)) isformed. “1” or “0” is selected for each of the additional parity bits p0through p10 so that each of the four 8-bits rows including the paritybits is an even parity code and that each of the seven 4-bit columnsincluding the parity bits is also an even parity code. Furthermore, “1”or “0” is selected for p0 so that p7 through p0 makes an even paritycode. That is to say, p10 through p0 are respectively given by thefollowing Equations (9) through (19):

p ₁₀ =b ₂₀ +b ₁₉ +b ₁₈ +b ₁₇ +b ₁₆ +b ₁₅ +b ₁₄  (Equation 9)

p ₉ =b ₁₃ +b ₁₂ +b ₁₁ +b ₁₀ +b ₉ +b ₈ +b ₇  (Equation 10)

p ₈ =b ₆ +b ₅ +b ₄ +b ₃ +b ₂ +b ₁ +b ₀  (Equation 11)

p ₇ =b ₂₀ +b ₁₃ +b ₆  (Equation 12)

p ₆ =b ₁₉ +b ₁₂ +b ₅  (Equation 13)

p ₅ =b ₁₈ +b ₁₁ +b ₄  (Equation 14)

p ₄ =b ₁₇ +b ₁₀ +b ₃  (Equation 15)

 p ₃ =b ₁₆ +b ₉ +b ₂  (Equation 16)

p ₂ =b ₁₅ +b ₈ +b ₁  (Equation 17)

p ₁ =b ₁₄ +b ₇ +b ₀  (Equation 18)

p ₀ =p ₇ +p ₆ +p ₅ +p ₄ +p ₃ +p ₂ +p ₁  (Equation 19)

As is well known in the art, an “even parity code” is a code whoseparity bits have been selected so that the number of ones included inthe codeword is an even number, and allows for 1-bit error detection.Also, the error may be detected just by obtaining an exclusive logicalsum of all information bits, thus simplifying the circuit configurationconsiderably. Suppose b18 has been inverted erroneously, for example. Inthat case, the error can be located by the parity bit p10 of the row towhich this error bit b18 belongs and by the parity bit p4 of the columnto which this error bit 18 belongs. Thus, by inverting b18 again afterit has been located, the error can be corrected.

As described above, on the optical disk of this embodiment, the addressinformation is arranged two-dimensionally and a simple parity code isused in each of these two directions, thereby increasing the errorcorrection ability even though a circuit for reading addresses therefromhas a small size.

Embodiment 16

Another embodiment of the optical disk medium according to the presentinvention will be described with reference to FIGS. 24(a) through 24(d).

FIG. 24(a) illustrates the recording surface 401 of the optical diskmedium, on which a spiral track groove 402 has been formed at apredetermined track pitch. Data is written thereon, or read therefrom,using a recording block 403 as the minimum unit.

Each recording block 403 is associated with positional information(i.e., address information) for use to locate the recording block. Inthis embodiment, each recording block 403 includes four positionalinformation units 404 as shown in FIG. 24(b).

On each of these positional information units 404, information about itsphysical location on the optical disk medium and its detection indiceshave been recorded in advance. In this embodiment, each of these piecesof information is represented by a combination of wobble shapes of thetrack groove, for example. The wobbled groove is formed during themanufacturing process of the optical disk medium. The positionalinformation that was once recorded as a combination of wobble patternsis non-rewritable.

In this manner, according to this embodiment, the positional informationof one recording block 403 as the minimum unit for data read and writeoperations is recorded in multiple areas of the block 403. Accordingly,if at least one of these pieces of positional information can bedetected, the recording block 403 can be located advantageously.

In this embodiment, each positional information unit 404 includesprecision positioning mark section 405, positional information section406 and sync mark section 407 as shown in FIG. 24(c). On the precisionpositioning mark section 405, a precision positioning mark (i.e.,identification mark), which is used as an index to absolute positioningduring a data write operation, has been formed. The precisionpositioning mark preferably has a structure similar to that of a blockmark according to any of the embodiments described above.

In writing data on the recording film of the optical disk using arecording apparatus, the precision positioning mark plays an importantrole. To improve the absolute positioning precision, the mark preferablyhas a shape to be detected as a signal having a relatively highfrequency.

On the positional information section 406 and the sync mark section 407,positional information and various other types of information have beenwritten by changing the wobble shape of the track groove 402. The changein wobble shape of the track groove may be represented by the change inamplitude, frequency and/or phase of the groove's displacement in thedisk radial direction. The wobble shapes to be adopted are determined sothat a signal corresponding to the positional information, which doesnot affect the recording data so easily and may be represented by thewobble of the track groove, is easily separable from a signalcorresponding to the data that has been written as a variation inquality of the recording film. More specifically, the frequency of thewobble signal preferably belongs to a frequency band that issufficiently lower than a frequency at which the data is written on therecording film. Also, as described above, various measures to identifythe wobble patterns highly accurately are preferably taken.

The sync mark section 407 is provided to establish bit synchronizationmore easily when the positional information recorded on the positionalinformation section 406 is read out. The sync mark section 407preferably has a groove shape that is not found anywhere in thepositional information section 406. Then, the sync mark section 407 canbe accurately detected at a higher probability, and erroneous detectionof bit synchronization can be prevented.

In a series of two positional information units 404, the precisionpositioning mark section 405 included in the latter positionalinformation unit 404 is placed just behind the sync mark section 407included in the former positional information unit 404 as shown in FIG.24(c).

According to this arrangement, the precision positioning mark in thesucceeding precision positioning mark section 405 can be detected highlyaccurately in accordance with the detection result of the sync marksection 407, which is easily detectable even by itself. Morespecifically, after a predetermined amount of time has passed since thesync mark section 407 was detected, a predicted detection window for theprecision positioning mark is opened. In this manner, only the precisionpositioning mark located inside the predicted detection window can bedetected. Then, the precision positioning mark will not be detectederroneously.

To achieve these effects, the precision positioning mark section 405 ispreferably placed just behind the sync mark section 407. For thisreason, in each positional information unit 404, the precisionpositioning mark section 405, positional information section 406 andsync mark section 407 are preferably arranged in this order (i.e., fromthe beginning toward the end of the unit 404) as shown in FIG. 24(c).

FIG. 24(d) illustrates a format for data to be written on an opticaldisk medium having such a track groove structure. To control therecording data in association with the positional information that hasbeen recorded on the disk, the data is read or written using therecording block 403 as a minimum unit.

Two contiguous recording blocks 403 are connected together by a linkingsection 408. The write operation is started or ended in the linkingsection 408. The location of each linking section 408 substantiallycorresponds to that of its associated precision positioning mark section405. A pattern including no user data is preferably written on thelinking section 408. Then, even if the signal written on the linkingsection 408 is affected due to an interference with the precisionpositioning mark, the read data will not be affected.

In the linking section 408 located at a writing start or end point, thedata written thereon is discontinued. Accordingly, to read out datastably enough, a VFO, i.e., a signal having a single frequency, ispreferably written on the linking section 408, for example.

Hereinafter, this embodiment will be described in further detail withreference to FIG. 25.

The recording surface 401 of the optical disk medium of this embodimenthas been coated with a phase change material, and a spiral track groove402 has been formed thereon at a track pitch of 0.32 μm. A dielectricfilm is further deposited to a thickness of 0.1 mm on the recordingsurface and is irradiated with a laser beam having a wavelength of 405nm through an objective lens with an NA of 0.85 during a read or writeoperation. The track groove 402 wobbles toward the inner and outerperipheries at a period of approximately 11.47 82 m. The wobble of thetrack groove can be detected as a push-pull signal. By multiplying thissignal by 186, a write clock signal for use in to perform a writeoperation at a substantially constant linear density (or at a channelbit length of 0.0617 μm (=11.47/186)) can be generated.

The track groove 402 is made up of a series of positional informationsegments 403. The user data is read or written by using an areacorresponding to each positional information segment 403 as the minimumunit. The data unit written on that area corresponding to one positionalinformation segment 403 is herein defined as the “recording block”.

The error correction, interleaving, alternation and other types ofprocessing are also executed using the recording block as the minimumunit. In this embodiment, one recording block includes 64 kilobytes ofuser data.

The recording data is provided with an additional error correction codeand is modulated in such a manner as to be written on the optical diskmedium appropriately. As the error correction code, a Reed-SolomonProduct Code for use in a DVD, for example, may be adopted. Therecording data may be modulated by an eight-to-sixteen modulationtechnique, for example. A SYNC (synchronization code) for establishingbit synchronization for a read signal and a VFO (variable frequencyoscillator) for locking a PLL are further added to the recording data.In this embodiment, the recording data has a channel bit length of1,243,968 bits.

Each positional information segment 403 is made up of four positionalinformation units 404, each of which consists of precision positioningmark section 405, positional information mark section 406 and sync marksection 407.

As shown in FIG. 26A, the precision positioning mark section 405 of thisembodiment is made of a series of eight sine wave wobbles 501 of thetrack groove. Also, in such a precision positioning mark section, amirror mark 601 is formed by discontinuing the track groove for apredetermined length at the second wave of the wobble as shown in FIG.27. The mirror mark 601 is detectable based on a fully added signalobtained by the reflection of a read laser beam from the disk.

The precision positioning mark may be used as an index for determiningthe absolute position for positional information detection or as anindex of the absolute position of data being written.

In this embodiment, the mirror mark 601 has a length of 2 bytes (i.e.,32 channel bits). The length of the mirror mark 601 is preferablydefined in such a manner as to minimize unwanted effects on adjacentparts of the track groove or on an interlayer part as for a dual-layerdisk, and may be set to 10 bytes (=10 μm) or less. However, the mirrormark 601 should also be long enough to be detectable sufficientlyaccurately, e.g., 1 byte (=1 μm) or more.

The location of the mirror mark 601 is preferably no earlier than thesecond wave of the wobble within the precision positioning mark section405 and no later than the fourth wave of the wobble to ensure highpositional accuracy for the window to be generated by detecting the syncmark section 407.

In this embodiment, the data write operation is started and ended insidethe precision positioning mark section 405. That is to say, theprecision positioning mark section 405 is associated with the linkingsection 408 used as a link between two blocks of the recording data.Then, the precision positioning mark is effectively applicable topositioning the recording data.

However, if the write operation is started and ended at that part wherethe mirror mark 601 exists, then the recording signal might be affectedby the mirror mark 601. In this embodiment, to prevent a substantivepart of the recording data from being affected by the mirror mark 601, aVFO is written on the precision positioning mark section 405.

Next, the location of the mirror mark 601 and the writing start/endpoints preferably satisfy the following relationships:

The writing start point should be behind the mirror mark in theprecision positioning mark section;

The writing end point should also be behind the mirror mark in theprecision positioning mark section;

The length between the beginning of the precision positioning marksection and the writing start point should be shorter than the lengthbetween the beginning of the precision positioning mark section and thewriting end point;

As for an optical disk medium to be subjected to repetitive writeoperations, the writing start and end points should be separated fromthe mirror mark to the extent that the mirror mark is not affected byany deterioration of the recording film due to the repetitive writeoperations; and

In view of a processing time delay that it takes for a recordingapparatus to actually start its write operation after having detectedthe mirror mark, the positional relationship between the mirror mark andthe writing start point should be determined.

Hereinafter, each of these conditions (A) through (E) will be describedin detail.

The condition (A) is laid down in view of the absolute positionalaccuracy of the writing start point. By setting the writing start point901 behind the mirror mark 601 in the precision positioning mark section405 as shown in FIG. 31A, the recording apparatus can start its writeoperation on detecting the mirror mark. Accordingly, the intendedpurpose of the mirror mark, i.e., indicating the beginning of a block,can be made full use of, thus improving the absolute positional accuracyof the writing start point.

The condition (B) is laid down in view of the absolute positionalaccuracy of the writing end point. By setting the writing end point 902behind the mirror mark 601 in the precision positioning mark section 405as shown in FIG. 31B, the recording apparatus can finish its writeoperation on detecting the mirror mark. Accordingly, the absolutepositional accuracy of the writing end point is improvable from the samepoint of view as that of the condition (A) on the writing start point.

The condition (C) requires that where the writing end and start pointsare located in the same precision positioning mark section, the writeoperation should be performed so that the writing end point 902 of theprevious recording block overlaps with the writing start point 901 ofthe next recording block as shown in FIG. 31C. By setting the writingstart and end points in this manner, no gap (i.e., unrecorded area) willbe left between the writing start and end points. If the write operationis carried out in such a manner as to leave an unrecorded area, then nosignal will be output from that unrecorded area while the recordedinformation is being read by a reproducing apparatus. As a result, thedigitization and clocking of the read signal temporarily lose itsstability disadvantageously. In contrast, if the write operation isperformed so that the writing start and end points always overlap witheach other, then the no read signal period is eliminated and the datacan be read out much more stably.

The condition (D) is laid down to prevent the mirror mark detection frombeing affected by so-called “writing start/end point deterioration”. Thewriting start/end point deterioration is a well-known phenomenon that isoften observed when the recording film of an optical disk medium is madeof a so-called “phase change material”, for example. Specifically, thisterm means that repetitive write operations on a recording film degradesor damages parts of the recording film around the writing start and endpoints due to the application of a thermal stress thereon. If areproducing apparatus reads out data from those degraded or damagedparts of a recording film, then a variation in the quantity of totallyreflected light is observed. Accordingly, if a mirror mark is locatedinside, or close to, the area where the writing start/end pointdeterioration has occurred, then the mirror mark detection might beaffected adversely. This is because it is difficult to tell a variationin the quantity of totally reflected light, indicating the presence of amirror mark, from the variation in the quantity of totally reflectedlight due to the start/end point deterioration. To eliminate theseunwanted effects, the mirror mark 601 may be placed so as to be distantfrom an area 903 that would be affected by the start point deteriorationaround the writing start point 901 as shown in FIG. 31D. Also, as shownin FIG. 31E, the mirror mark 601 may be placed so as to be distant froman area 904 that would be affected by the end point deterioration aroundthe writing end point 902.

The condition (E) is a more strict definition of the condition (A) andrequires that the length between the mirror mark and the writing startpoint should be determined in view of a processing time delay necessaryfor the drive. Examples of the drive's processing time delays include: aprocessing time delay caused by a means for detecting the mirror mark; aprocessing time delay it takes to correct synchronization after havingdetected the mirror mark; and a time it takes to prepare for generatinga write laser power at a required level. By setting the writing startpoint with these processing time delays into account, the intendedpurpose of the mirror mark as described for the condition (A), i.e.,improvement in absolute positional accuracy of the writing start point,is accomplished effectively.

Furthermore, each of the positional information mark section 406 and thesync mark section 407 is a collection of subdivided information units408, each being a series of 32 wobble waves of the same shape. Thepositional information mark section 406 includes a series of 48subdivided information units, in each of which one-bit information of“1” or “0” is represented as a piece of subdivided information by awobble having steep inner- or outer-periphery-oriented displacements asshown in FIGS. 26B and 26C, thereby making 48-bit positional informationand its error detection code.

In this case, to detect the positional information from the positionalinformation mark section, the beginning of the positional informationmark section should be located. For that purpose, the mirror mark 601 inthe precision positioning mark section 405 is used. However, the mirrormark 601 by itself might be detected erroneously or might be missed. Onthe optical disk medium of the present invention, the precisionpositioning mark section 405 of the succeeding positional informationunit 404 is placed just behind the sync mark section 407. Accordingly,the location of the mirror mark 601 existing in the precisionpositioning mark section 405 can be narrowed accurately by detecting thesync mark. As a result, the mirror mark 601 required for specifying theabsolute position is detectable highly accurately.

The sync mark section 407 is made up of a series of four subdividedinformation units 408, each of which is represented by a wobble havingsteep inner- and outer-periphery-oriented displacements or by a wobbleshowing a sine waveform for both the inner- and outer-periphery-orienteddisplacements. FIGS. 28A through 28E illustrate exemplary wobble shapesof the sync mark section 407. The sync mark section 407 is a combinationof wobbles 504 having steep inner- and outer-periphery-orienteddisplacements as shown in FIG. 26D (which will be herein referred to as“bi-rectangular wobbles”) and wobbles 501 in a sine waveform as shown inFIG. 26A (which will be herein referred to as “sine wave wobbles”). InFIGS. 28A through 28E, the bi-rectangular wobbles 504 are identified by“S” while the sine wave wobbles 501 are identified by “B”.

In FIG. 28A, the four subdivided information units are all representedby the bi-rectangular wobbles 504. That is to say, since the wobbles ofthe same shape realize high continuity, the sync mark section isdetectable highly accurately. In FIGS. 28B and 28C, the bi-rectangularand sine wave wobbles 504 and 501 are alternated on a subdividedinformation unit basis. In these patterns, there are many wobble shapechange points, thus ensuring high absolute positional accuracy. In FIGS.28D and 28E, bi-rectangular wobble, sine wave wobble, sine wave wobbleand bi-rectangular wobble are arranged in this order (or to form theopposite pattern). Each of these arrangements has one change point atwhich the bi-rectangular wobble 504 is replaced by the sine wave wobble501 and one change point at which the sine wave wobble 501 is replacedby the bi-rectangular wobble 504. Accordingly, the arrangements withsuch a positional relationship ensure increased reliability againsterroneous detection of the absolute position.

On the optical disk medium of this embodiment, each positionalinformation segment, corresponding to one recording block unit, is madeup of four positional information units. However, the present inventionis not limited to this specific embodiment, but each positionalinformation segment may be made up of a number L (which is a naturalnumber) of positional information units.

Suppose the amount of information included in each positionalinformation section 406 is A bits,

each sync mark section 407 has a length corresponding to B wobbleperiods,

each precision positioning mark section 405 has a length correspondingto C wobble periods,

each subdivided information unit has a length corresponding to M wobbleperiods,

one wobble period is W times as long as one channel bit of the recordingdata,

the number of channel bits included in each recording block is D and

the number of positional information units included in each positionalinformation segment is E.

In this case, A, B, C, D, E, M and W are all natural numbers and aredetermined so as to satisfy the following Equation (20):

 D=(A×M+B+C)×W×E  (Equation 20)

In this embodiment, in accordance with an eight-to-sixteen modulationtechnique, which is well known as a technique of generating a modulationcode for a recording signal, one wobble period has a lengthcorresponding to 186 channel bits (i.e., W=186). Also, each precisionpositioning mark section 405 has a length corresponding to 8 wobbleperiods and each subdivided information unit 408 has a lengthcorresponding to 32 wobble periods (i.e., C=8 and M=32). However, thepresent invention is not limited to this specific embodiment. Forexample, when a modulation code for converting 8 bits into 15 bits isused, one wobble period may have a length corresponding to 155 channelbits. Also, each precision positioning mark section 405 may have alength corresponding to 9 wobble periods and each subdivided informationunit 408 may have a length corresponding to 36 wobble periods.

Where a modulation code for converting 2 bits into 3 bits (i.e.,converting 8 bits into 12 bits) is used as in the well-known (1, 7)modulation technique, one wobble period may have a length correspondingto 186 channel bits, each precision positioning mark section 405 mayhave a length corresponding to 6 wobble periods and each subdividedinformation unit 408 may have a length corresponding to 24 wobbleperiods. Alternatively, one wobble period, each precision positioningmark section 405 and each subdivided information unit 408 may correspondto 124 channel bits, 9 wobble periods and 36 wobble periods,respectively.

That is to say, where a modulation code for converting 8 bits into Fchannel bits is used,

one wobble period is supposed to have a length corresponding to Wchannel bits;

each precision positioning mark section 405 is supposed to have a lengthcorresponding to C wobble periods; and each subdivided information unit408 is supposed to have a length corresponding to M wobble periods.

In this case, if the optical disk medium is formed so as to satisfy thefollowing Equations (21) and (22):

P×R×F=C×W  (Equation 21)

Q×R×F=M×W  (Equation 22)

then each precision positioning mark section 405, each positionalinformation section 406 and each sync mark section 407 may haverespective lengths corresponding to the wobble wave numbers defined inthis embodiment.

In Equations (21) and (22), P and Q are rational numbers and R is anatural number. P means that each precision positioning mark section hasa length corresponding to P frames of the recording data. In thisembodiment, P=1. Q means that each subdivided information unit has alength corresponding to Q frames of the recording data. In thisembodiment, Q=4. R is the number of bytes of one frame of the recordingdata. In this embodiment, R=93. It should be noted that a relationshipP:Q=C:M is derived from Equations (21) and (22).

In this configuration, a wobbling groove (including the positionalinformation and mirror marks) that has been pre-cut on an optical diskmedium can be easily associated with the recording data. As a result, arecording apparatus and a reproducing apparatus for an optical diskmedium according to this embodiment may have a simplified configuration.Also, P and Q may be rational numbers but are more preferably integers.

On the optical disk medium of this embodiment, the mirror mark 601 isprovided as a precision positioning mark for each and every precisionpositioning mark section 405 to detect the positional information moreaccurately. Alternatively, to reduce the unwanted effects of the mirrormarks 601 on adjacent parts of the track or on interlayer parts of adual-layer disk, only the precision positioning mark section 405 in thepositional information unit 404 located at the beginning of eachpositional information segment may have the mirror mark 601.

The precision positioning mark is not limited to the mirror mark used inthis embodiment, but may be any other mark so long as the markcontributes to obtaining a detection signal with high positioningaccuracy and is easily distinguishable from a signal for obtainingpositional information. For example, a wobble, having a periodsufficiently shorter than that of a wobble that has been formed torepresent positional information, may be provided as a precisionpositioning mark. Also, an isolated pit may be formed as an alternativeprecision positioning mark between adjacent parts of the wobbled groove(i.e., on a “land”).

In this embodiment, the subdivided information “1” is represented by awobble pattern having steep inner-periphery-oriented displacements, thesubdivided information “0” is represented by a wobble pattern havingsteep outer-periphery-oriented displacements and the sync mark sectionis made of a combination of bi-rectangular wobbles S and sine wavewobbles B. Accordingly, the information bits “1” and “0” aredistinguishable by a maximum Euclidean distance and the pieces ofinformation “B” and “S” are also distinguishable by a maximum Euclideandistance. Thus, to achieve similar effects, the information bits “1” and“0” may be represented by bi-rectangular and sine wave wobbles,respectively, and “B” and “S” of the sync mark may be represented by awobble pattern having steep outer-periphery-oriented displacements and awobble pattern having steep inner-periphery-oriented displacements,respectively.

Also, in this embodiment, the sync marks and positional information arerecorded using all of the four types of wobble patterns (i.e., sine wavewobble pattern, bi-rectangular wobble pattern, wobble pattern with steepinner-periphery-oriented displacements and wobble pattern with steepouter-periphery-oriented displacements). However, the present inventionis not limited thereto. For example, only two out of these four (e.g.,wobble pattern with steep inner-periphery-oriented displacements andwobble pattern with steep outer-periphery-oriented displacements) may beused or three wobble patterns may also be used. When just two types ofwobble patterns are used, the sync marks and the positional informationare preferably distinguishable from each other more easily. For thatpurpose, the positional information may be modulated in accordance witha predetermined modulation rule and unique patterns, not defined by themodulation rule, may be placed as the sync marks.

Furthermore, in this embodiment, the track groove is wobbled at a singleperiod, and the positional information and sync marks are recorded bychanging the shapes of the wobbling displacements (i.e., by making thedisplacements smooth or steep). However, the improvement in detectionaccuracy of the precision positioning mark as achieved by placing thesync mark ahead of the precision positioning mark is not limited by thetypes of wobble patterns of the track groove. Alternatively, theconfiguration of this embodiment is also applicable to an optical diskof the type recording addresses and other types of information thereonby changing the wobble period, phase or amplitude of the track groove orby changing the width or depth of the groove, for example.

As described above, if the precision positioning mark section,positional information section and sync mark section are arranged inthis order in each positional information unit, then the precisionpositioning mark (e.g., mirror mark) included in the precisionpositioning mark section of one positional information unit is locatedjust behind the sync mark section of the previous positional informationunit. Accordingly, based on the detection result of the preceding syncmark section, the precision positioning mark (e.g., mirror mark) placedat the beginning of the succeeding positional information unit can bedetected more accurately.

Next, exemplary recording data formats according to this embodiment willbe described with reference to FIGS. 31A through 31C. FIG. 31A shows adata format for a recording block at a writing start point; FIG. 31Bshows a data format for a recording block under a continuous writeoperation; and FIG. 31C shows a data format for a recording block at awriting end point.

In FIGS. 31A through 31C, each of the data fields Data field 1, Datafield 2, Data field 3 and Data field 4 has a length of 19,344 bytes, inwhich 208 consecutive frame regions (not shown), each having a length of93 bytes, are arranged. Each 93-byte frame region is made up of a 2-byteSYNC code placed at the beginning and 91-byte modulated recording data.Accordingly, the maximum amount of recording data is 91×208=18,928bytes. However, the amount of user data actually writable is 16kilobytes, to which parity bits for use in error correction ordetection, redundant data (e.g., IDs for identifying the recording datapositions) and so on are added.

Each of the VFO fields VFO1, VFO2 and VFO3 is a field for use to lock aPLL needed to operate the reproducing apparatus, and no user data iswritten on any of these fields. On each VFO field, to establish bitsynchronization more easily by locking the PLL at a high speed, marksand spaces are preferably recorded repeatedly at a fixed channel bitlength, for example.

Each PA field PA functions as a connection to the end of the previousdata field. For example, where a well-known run-length-limited (RLL)code is used as a modulation code for the data fields, the PA fieldcontributes not only to satisfying the run-length limitation even at theconnection to the end of the previous data field but also to decodingthe end of the previous data field properly during a read operation.

Each PS field PS contributes to detecting the beginning of thesucceeding data field more accurately and establishing the bytesynchronization more firmly. A pattern that is not easily detectederroneously as any other field (i.e., data field, VFO field or PAfield), e.g., a unique pattern not existing in any other field, or apattern having too steep auto-correlation characteristic to match thatof any other field even if the bits thereof are shifted may be recordedas the PS field PS.

Each of the recording blocks shown in FIGS. 31A through 31C correspondsto the positional information segment 403 shown in FIG. 25. And therespective data fields are recorded so as to be associated with thepositional information units 404. That is to say, each of the datafields Data field 1, Data field 2, Data field 3 and Data field 4 isrecorded so as to have a length corresponding to the combined length ofthe positional information section and the sync mark section inassociated one of the four positional information units 404 that make upone positional information segment 403. Also, the combined length of PA,VFO2 and PS is 93 bytes, and these fields are recorded so as to have alength equal to that of the precision positioning mark section 405.

Furthermore, as shown in FIG. 31A, VFO3, i.e., one of the VFO fieldsthat is located at the end of the recording block at the writing startpoint, has a length of 41 bytes. Also, as shown in FIG. 31B, VFO1, whichis located at the beginning of the recording block under the continuouswrite operation, has a length of 45 bytes. The combined length of theseVFO fields is 86 bytes, which is equal to that of VFO2. In the same way,as shown in FIG. 31B, VFO3, which is located at the end of the recordingblock under the continuous write operation, has a length of 41 bytes.Also, as shown in FIG. 31C, VFO1, which is located at the beginning ofthe recording block at the writing end point, has a length of 45 bytes.The combined length of these VFO fields is 86 bytes, which is also equalto that of VFO2. Accordingly, at either connection between two recordingblocks under the continuous write operation, the total length of PA,VFO3, VFO1 and PS is also 93 bytes, which is equal to the length of theprecision positioning mark section 405.

In this manner, data can be written in association with the positionalinformation that has been pre-cut on an optical disk medium, and thedata written can also be located by reference to the positionalinformation.

The length of 93 bytes of the precision positioning mark section 405 isequal to the length of each of the frame regions that make up one datafield. Accordingly, the precision positioning mark section under thecontinuous write operation, i.e., a part where PA, VFO and PS arerecorded, may be handled as one frame region. Thus, even in a connectionbetween two adjacent data fields, frame synchronization can beestablished as in a data field, thereby simplifying the read operationof the reproducing apparatus.

FIG. 32 illustrates an exemplary method for writing data at writingstart and end points. FIG. 32(a) illustrates a sine wave wobble and amirror mark that have been pre-cut for a precision positioning marksection. In the example illustrated in FIG. 32, a known (1, 7)modulation code is supposed to be used as a modulation code, one byte issupposed to be 12 channel bits, one wobble period is supposed to have alength of 124 channel bits and the precision positioning mark section issupposed to have a length corresponding to 9 wobble periods. Also, theprecision positioning mark section is supposed to start at a peak of thesine wave wobble and the mirror mark is supposed to start at the 22^(nd)byte as counted from the start point of the precision positioning marksection and have a width of 2 bytes.

In this case, the length between the start point of the precisionpositioning mark section and the center of the mirror mark 601 (at the23^(rd) byte) is (23×12)÷124≈2.23, which is approximately equal to 2.25wobble periods. Accordingly, as shown in FIG. 32(a), the center of themirror mark 601 substantially matches a falling zero-crossing point ofthe third wave of the sine wave wobble.

FIG. 32(b) illustrates a recording block at a writing start point. Inthis example, after a VFO field VFO1 has been recorded for (45+k) bytes,PS field and data field Data field 1 are recorded continuously, where kis an integer between 0 and 7. For example, if the integer k is newlyset at random every time the recording apparatus writes data, then therecording film is less likely deteriorated because the same data willnot be repeatedly written at the same position.

FIG. 32(c) illustrates a writing end point of the recording block. Inthis example, the data field Data field 4 is followed by a PA field, andthen a VFO field VFO3 is finally recorded for (50−k′) bytes, where k′ isalso an integer between 0 and 7. Then, the recording film is also lesslikely deteriorated even at the writing end point. This k′ value may beset equal to the k value at the writing start point. Or mutuallydifferent values may be used for the writing start and end points.

Where a modulation code for converting 8 bits into F channel bits isadopted, the length between the end of the mirror mark and the writingstart point (i.e., the start point of VFO1) is preferably (20+j/F)bytes, where j is an integer from 0 to (F−1). For example, if theinteger j is newly set at random every time the recording apparatuswrites data, then the deterioration of the recording film at the writingstart point is suppressible even when the same data is repeatedlywritten at the same position.

In this embodiment, if the repetitive writing is performed, thestart/end point deterioration of the recording film is supposed to occurin an area of G bytes after the writing start point and in an area of Gbytes before the writing end point.

The length as measured from the end of the mirror mark is determined soas to satisfy the conditions (A), (D) and (E). In other words, if theinteger j is defined within the above-described range, then the lengthbetween the end of the mirror mark and the writing start point will be20 bytes or more but less than 21 bytes. Thus, the length can be noshorter than 20 bytes. A length like this is sufficiently long even inview of the area where the writing start point deterioration may occuror the processing time delay it takes for the recording apparatus toactually start its write operation after having detected the mirrormark.

On the other hand, the length between the end of the mirror mark and thewriting end point (i.e., the end point of VFO3) is 29 bytes. Where thewrite operation has been performed ideally at a writing positionalaccuracy of zero, the length of G bytes of the area where the writingend point deterioration may occur should preferably be smaller than 29.Then, the condition (D) that the mirror mark should be sufficientlyseparated from the writing end point deterioration area is satisfied.Obviously this arrangement also satisfies the condition (B).

Also, the length between the beginning of the precision positioning marksection and the writing start point is (44+j/F) bytes, while the lengthbetween the beginning of the precision positioning mark section and thewriting end point is (53+j/F) bytes. The difference between theselengths is 9 bytes. That is to say, the condition (C) is satisfied.Where the write operation has been performed ideally at a writingpositional accuracy of zero, the writing start and end points have anoverlap of 9 bytes. In that case, even if the shifts of the writingpoints reach 9 bytes in total, no non-recorded areas will be left.

If the data writing start/end points are set in this manner, theresultant positional relationships satisfy all of the conditions (A)through (E) described above. Accordingly, the “improvement in positionalaccuracy of writing start/end points” is accomplished effectively.

It should be noted that the VFO field VFO1 is used in the reproducingapparatus to digitize the read data and to lock the PLL. However, anarea having a length of (45−G) bytes is actually usable for thesepurposes.

Embodiment 18

An optical disk read/write drive for reading an address on an opticaldisk medium according to a seventeenth embodiment will be described withreference to FIG. 29. In FIG. 29, an optical head for detecting a signalbased on the brightness or darkness of an optical disk medium 1 bycondensing a laser beam onto the disk 1 so that the light spot formedthereon can follow up the track groove of the optical disk 1 isidentified by 801. A read signal processing section for generating afully added signal and a wobble signal by performing operationprocessing on the detection signal of the optical head 801 is identifiedby 802. The wobble signal is supposed to appear as a positive signal asfor the inner periphery and as a negative signal as for the outerperiphery. A subdivided information detecting section outputs “1” ondetecting a wobble signal in which only the rising displacements aresteep and outputs “0” on detecting a wobble signal in which only thefalling displacements are steep.

In this case, once a focus control section and a tracking controlsection (neither of which is shown in FIG. 29) have established such acontrol that the light spot follows up the track groove, the opticaldisk read/write drive of this embodiment needs to detect the positionalinformation to locate its absolute position on the track groove.Hereinafter, it will be described how the read/write drive operates todetect the positional information.

FIG. 33 is a flowchart illustrating exemplary positional informationreading processing performed by the optical disk read/write drive ofthis embodiment. First, a sync mark is detected at a sync mark section(Step 1). Once the sync mark has been detected, positional informationcoarsely synchronized state is supposed to have been established topredict an interval, during which the succeeding precision positioningmark (i.e., mirror mark) should appear, based on the detection result ofthe sync mark (Step 2). If the precision positioning mark (mirror mark)is detected during the predicted interval (Step 3), then positionalinformation precisely synchronized state is supposed to have beenestablished to predict the division between subdivided information units(i.e., bit division of the positional information) based on thedetection result of the precision positioning mark (Step 4). On theother hand, if no precision positioning mark is detected even after thepredicted interval has passed, then the division between subdividedinformation units (i.e., bit division of the positional information) ispredicted based on the detection result of the sync mark while thepositional information is still coarsely synchronized. Then, thepositional information is read out from the positional informationsection according to the divisions predicted (Step 5).

As can be seen, if the precision positioning mark (mirror mark) has beendetected, the division of the subdivided information is predictableaccurately enough. As a result, the number of detection errors of thepositional information can be reduced. In addition, even if no precisionpositioning marks (mirror marks) have been detected, the division of thesubdivided information is still predictable based on the detectionresult of the sync mark.

In the processing flow illustrated in FIG. 33, if no sync marks aredetected in Step 1, the detection of the precision positioning mark isnot started until the sync mark is detected. Alternatively, thisprocessing flow may be modified in such a manner as to use the sync markthat has been detected from a block preceding the current block. FIG. 34is a flowchart illustrating exemplary positional information readingprocessing including this alternative processing step.

In FIG. 34, if no sync marks have been detected in Step 1, then it isdetermined whether or not any sync mark has been detected from a numberN (which is a natural number) of preceding blocks (Step 6). If theanswer is YES, then the processing jumps to the processing step ofdetecting the precision positioning mark (mirror mark). That is to say,even if no sync marks have been detected from the current block, thepositional information coarsely synchronized state may be interpolatedbased on the detection results of the preceding N blocks. Accordingly,it is possible to avoid the unwanted situation where no positionalinformation can be read out from the current block because no sync markhas been detected yet. It should be noted that the parameter N indicatesthe number of blocks on which the coarsely synchronized state should beinterpolated. Thus, the greater the parameter N, the longer the coarselysynchronized state should be interpolated. However, if N is excessivelylarge, then the positional information might be out of synchronizationdue to the effects of a number of variable factors. For that reason, Nshould be set to an optimum value in view of the performance of thedrive and the properties of the optical disk medium.

Also, the positional information read out and/or the error detectionresult thereof may also be used as a condition for establishing thepositional information coarsely or precisely synchronized state. Forexample, if errors have been detected from the positional information ofseveral consecutive blocks (e.g., parity error detection) or if thepositional information values (i.e., addresses) are discontinuous amonga series of blocks, then the coarsely or precisely synchronized statemay be once canceled to try to establish a synchronized state again.

This processing flow will be described through the operation of thedrive shown in FIG. 29.

On detecting a wobble signal in which the rising and fallingdisplacements are both steep, a sync mark detecting section 804 outputsa sync mark detection signal. In accordance with the timing of the syncmark that has been detected by the sync mark detecting section 804, afirst window detecting section 809 generates a detection window thatwill have a predetermined time width after a prescribed amount of timehas passed since a point in time at which the mirror mark should appear.When the fully added signal reaches a predetermined level or more duringthe interval of the detection window that has been generated by thefirst window detecting section 809, a mirror mark detecting section 805outputs a mirror mark position signal. On the optical disk medium of thefirst embodiment, the mirror mark exists in the precision positioningmark section just behind the sync mark. Accordingly, the detectionwindow can be narrowed and the erroneous detection can be prevented.

If the mirror mark detecting section 805 has detected the mirror markduring the detection window that has been generated by the first windowdetecting section 809, then a positional information synchronizingsection 807 generates a subdivided information division timing fordetecting the positional information in accordance with the timing. Onthe other hand, if the detecting section 805 has detected no mirrormarks during that interval, then the synchronizing section 807 generatesthe subdivided information division timing for detecting the positionalinformation based on the timing of the detection window. In that case,the detection accuracy and error rate are inferior compared to thesituation where the mirror mark has been detected. However, it is stillpossible to locate the positional information. In accordance with thesubdivided information division timing that has been generated by thepositional information synchronizing section, a positional informationdetecting section 808 determines the subdivided information to be “1” or“0”, thereby detecting address information.

In this case, once the mirror mark and the positional information havebeen detected (with no errors), then the position at which the mirrormark has been detected may be regarded as correct. Accordingly, byfurther narrowing the mirror mark detection window of the nextpositional information unit on the same track groove, the erroneousdetection can be further suppressed.

In recording information, a system control section 810 issues a writeinstruction to a write section 806. The write section 806 specifies awriting start point and a writing end point in accordance with theabsolute position that has been determined from the position at whichthe mirror mark has been detected. Then, the write section 806 makes theoptical head 801 emit an intense laser beam to record the information.

FIG. 35 is a flowchart illustrating exemplary data writing processingperformed by the optical disk read/write drive of this embodiment.

In FIG. 35, Steps 1 through 6 are the same as the counterparts of thepositional information reading processing as already described withreference to FIGS. 33 and 34. By performing these processing steps 1through 6, the positional information (i.e., address) is read out andthe position at which the positional information (address) read outshould be recorded is indicated. That is to say, based on the addressread out, it is determined whether or not the next block is the target,or the block to be written (Step 7). If it has been determined that theaddress of the next block is not that of the target, then the processingreturns to Step 1 to restart the positional information readingprocessing (Steps 1 through 6). On the other hand, if it has beendetermined that the address is the target address, then the processingadvances to Step 8 of determining whether or not a preciselysynchronized state has been established. If it is determined, based onthe state of the precision positioning mark detected, that the preciselysynchronized state has already been established, then a timing to startthe data write operation is determined based on the precisionpositioning mark detected and then the write operation is carried out(Step 9). However, if it is determined that the precisely synchronizedstate has not yet been established, then the processing returns to theprevious part of the track to perform re-positioning processing (Step10).

Also, if the mirror mark and positional information of the previouspositional information segment have already been detected, the writingstart and end points of the current segment may be set by interpolatingthe mirror mark of the previous segment even when no mirror mark isdetected at the beginning of the current segment.

It should be noted that the positional information read out or the errordetection result thereof may be used as a condition for determiningwhether the precisely synchronized state has been established beforestarting the write process. For example, if errors have been detectedconsecutively from the positional information of the current block orprevious several blocks (e.g., parity error detection) or if thepositional information (i.e., addresses) values are discontinuous amonga series of blocks, then the write operation does not have to be startedbut the re-positioning process may be carried out even if the precisionpositioning mark has already been detected.

As described above, according to the address information reproducingapparatus of this embodiment, the precision positioning mark (i.e.,mirror mark) for specifying the absolute position exists just behind thesync mark section that is placed at the end of the previous positionalinformation unit. Accordingly, by detecting the sync mark, generatingthe detection window of the precision positioning mark (mirror mark)based on its timing, and immediately detecting the precision positioningmark (mirror mark), the precision positioning mark (mirror mark) can bedetected much more accurately and the positional information can be readout far more reliably.

In the same way, according to the optical disk recording apparatus ofthis embodiment, the location of the precision positioning mark (mirrormark) to be detected in starting to write data can also be narrowedhighly accurately based on the detection result of the sync mark. As aresult, the data writing start and end points can also be set much moreprecisely.

Embodiment 19

Hereinafter, an embodiment of recording “control information”, which isusually recorded on a lead-in area, for example, as a combination ofvarious groove shapes will be described.

On a known DVD-RAM, control information is recorded as physicallyembossed, uneven pre-pits in a control information area within a lead-inarea. The control information typically refers to physical formatinformation, disk manufacturing information, copyright protectioninformation and so on. The physical format information includesinformation required for determining the power of the laser radiation tobe irradiated onto the optical disk medium during read and writeoperations and for compensating for the power. The disk manufacturinginformation includes information about the manufacturer of the opticaldisk medium, the manufacturing lot thereof and so on. The copyrightprotection information includes key information necessary for encryptionand/or decoding. These types of control information have been recordedas pits.

In the preferred embodiments of the present invention described above,the positional information is recorded by wobbling the groove in theuser area (i.e., data area) and by combining various groove (or wobblewave) shapes with each other. This embodiment is characterized byrecording the control information as a combination of wobble patterns ofthe wobbling groove on the lead-in and/or lead-out area(s) during themanufacturing process of the optical disk medium.

Hereinafter, this embodiment will be described with reference to theaccompanying drawings.

First, referring to FIG. 36, illustrated is a configuration for anoptical disk medium according to this embodiment. The recording surface401 of the optical disk medium shown in FIG. 36 has been coated with aphase change material, and a spiral track groove 1502 has been formedthereon at a track pitch of 0.32 μm. A dielectric film is furtherdeposited to a thickness of 0.1 mm on the recording surface and isirradiated with a laser beam having a wavelength of 405 nm through anobjective lens with an NA of 0.85 during read and write operations.

In the lead-in area that is located closer to the inner periphery thanthe user data area is, a track groove 1502 for recording at leastcontrol information thereon has been formed. This track groove 1502 iscontinuous with the track groove 402 located in the user area as shownin FIG. 25. Like the track groove 402, the track groove 1502 located inthe lead-in area also wobbles toward the inner and outer peripheries ata period of approximately 11.47 μm.

The track groove 1502 is made up of a series of positional informationunits or a plurality of positional information segments, each includingmultiple positional information units. Each positional information unitincludes a plurality of subdivided information units 408 that arearranged along the groove. In these respects, the track grooves 1502 and402 have similar configurations.

On each of the subdivided information units 408 on the track groove1502, one-bit information constituting positional information (i.e.,positional information element 1503) and control information elements1505 constituting the control information of the optical disk mediumhave been recorded.

In this embodiment, the positional information element 1503 isrepresented by the wobble shape of the first half of the subdividedinformation unit 408, while the control information elements 1505 arerepresented by the wobble shapes of the second half of the subdividedinformation unit 408.

In the example illustrated in FIG. 36, the positional informationelement 1503 representing one-bit positional information of “1” or “0”has been recorded as a wobble having 16 periods. More specifically, “0”is represented by a wobble having rectangular inner-periphery-orienteddisplacements, while “1” is represented by a wobble having rectangularouter-periphery-oriented displacements. In this example, to read asignal more reliably, wobbles of the same shape have been formed over 16wobble periods, thereby representing the one-bit positional informationelement 1503 collectively.

As for the control information on the other hand, by combining these twotypes of wobbles with each other, one-bit control information element isrepresented as “0” or “1” for 4 wobble periods. In the exampleillustrated in FIG. 36, a control information element of “0” isrepresented by 4 wobble periods of “0”→“0”→“1”→“1”, while a controlinformation element of “1” is represented by 4 wobble periods of“1”→“1”→“0”→“0”. That is to say, each one-bit control informationelement is represented by a bi-phase code, which uses two wobble periodsas a unit, on a four wobble period basis. In the example illustrated inFIG. 36, four-bit control information elements are recorded in eachsubdivided information unit 408. However, the bi-phase code unit is notlimited to two wobble periods, but may be determined appropriately inview of the amount of control information needed and the degree ofreliable detection. If the amount of information needed is relativelysmall, then the information may be read out even more reliably byadopting a bi-phase code that uses 8 wobble periods as a unit. Also, thepositional information element and the control information elements thatare included in each subdivided information unit do not have to have thewobble numbers used in this example. Instead, those wobble numbers maybe appropriately determined depending on respective reliability weightsof the positional and control information.

If this bi-phase coding method is adopted, the number of wobblesrepresenting “0” is equal to the number of wobbles representing “1” inthe second half of each subdivided information unit 408 on which thecontrol information has been recorded. Accordingly, if a method ofdetermining the one-bit positional information element by majority(specifically by determining each of the wobbles over 16 periods to be“0” or “1”) is used to read out the positional information element, thedecision of the positional information element (i.e., the decision bymajority) is not affected at all by the contents of the controlinformation.

The positional information of each positional information unit (i.e.,block) is read as multi-bit positional information elements 1503obtained from a plurality of subdivided information units, while thecontrol information of the disk is read as multi-bit control informationelements 1505.

In recording control information by the known embossing method, if thedepth of the groove is shallower than ⅙ of the wavelength λ of the readlaser radiation, then the amplitude of the read signal, as representedby the presence or absence of the embossment, tends to decrease. On theother hand, to increase the amplitude of the read signal representinguser information, the groove depth should be as shallow as about λ/12.Accordingly, if the groove depth is set at λ/12 to respect the accuracyof the user information read out, then it is very difficult to read thecontrol information that has been recorded as embossed shapes.

In contrast, according to this embodiment, the control information isrecorded as a combination of groove wobble shapes. Thus, even if thegroove is shallow, the control information can be read with sufficientlyhigh reliability.

Next, a configuration for an optical disk read/write drive will bedescribed with reference to FIG. 39.

Unlike the drive shown in FIG. 29, the optical disk read/write driveshown in FIG. 39 further includes: a control information elementdetecting section 812 for detecting control information elements fromthe output of the read signal processing section 802; and a controlinformation detecting section 814 for detecting control information fromthe control information elements obtained.

The control information element detecting section 812 is implemented asa circuit having the same configuration as the subdivided informationdetecting section 803. On detecting a wobble signal in which only risingdisplacements are steep, the control information element detectingsection 812 outputs “1”. On the other hand, on detecting a wobble signalin which only falling displacements are steep, the control informationelement detecting section 812 outputs “0”. The control informationdetecting section 814 has the same configuration as the positionalinformation detecting section 807. In accordance with the subdividedinformation division timing that has been generated by the positionalinformation synchronizing section 808, the control information detectingsection 814 determines the subdivided information to be “1” or “0”,thereby detecting the control information. Then, the control informationis sent out to the system control section 810.

As described above, according to this embodiment, not only a clocksignal but also address information and control information can begenerated or read out from the wobble shapes of the groove. Preferably,no user data should be written on the area where such controlinformation is written. No user data is written on the lead-in orlead-out area of the optical disk. Accordingly, the control informationis preferably written within the lead-in or lead-out area.

As for the groove on which no user data is written, no user data issuperposed on the read signal. Accordingly, positional information orcontrol information can be extracted from the read signal highlyreliably. For that reason, one-bit information may be recorded on thenon-user area at a smaller number of wobbles (or waves) compared to theuser area. Thus, in this embodiment, the number of wobbles (or waves)needed for representing each one-bit positional information element 503is 18, which is half as small as the number of wobbles needed forrepresenting one-bit subdivided information “1” or “0” in the user area.However, the information still can be read reliably enough.

Also, in the non-user area, the magnitude of wobble (i.e., the amplitudeof wobble in the radial direction) of the groove on which the controlinformation should be written may be greater than (e.g., twice as largeas) the magnitude of wobble in the user area. Stated otherwise, if thewobble signal can be read safely even if data has already been writtenthereon, then the control information and other types of information tobe added may be recorded on the track groove 1502.

Next, other exemplary control information recording formats will bedescribed with reference to FIGS. 37A through 37E.

In the example illustrated in FIG. 37A, one-bit control informationelement is allocated to each single wobble period. The wobble shape foreach single wobble period represents “1” or “0”. Thus, compared to theexample illustrated in FIG. 37, the amount of information increasesfourfold.

In the example illustrated in FIG. 37B, one-bit control informationelement is also allocated to each single wobble period. In this respect,the example shown in FIG. 37B is the same as the example shown in FIG.37A. However, unlike the example shown in FIG. 37A, the wobble shape foreach single wobble period represents “B” or “S”. According to thisexample, the control information is easily distinguishable from thesubdivided information to be represented as “1” or “0”.

In the example illustrated in FIG. 37C, a bi-phase code for representingone bit for 2 wobble periods is adopted. Thus, compared to the exampleillustrated in FIG. 37, the amount of information can be doubled.

In the example illustrated in FIG. 37D, “1” and “0” of the example shownin FIG. 37C are replaced with “B” and “S”, respectively.

In the example illustrated in FIG. 37E, two-bit information items “11”,“00”, “01” and “10” are recorded by using four types of wobble shapes“S”, “B” “1” and “0”. To increase the reliability, each wobble shape isrepeatedly recorded twice for two wobble periods.

Next, FIG. 38 will be referred to. In the example illustrated in FIG.38, one positional information segment 403 includes four positionalinformation units. In one of these four positional information unitsthat is located at the beginning of the segment 403, the “positionalinformation” of this positional information segment 403 is recorded inthe positional information section thereof. In the other threepositional information units, the “control information” of the segment403 is recorded in the positional information section thereof. Each ofthese positional information units includes identification informationindicating whether the information recorded in the positionalinformation section thereof represents the “positional information” orthe “control information”.

As described above, if the precision positioning mark section is placedjust behind the sync mark section in a series of positional informationunits, then the division of the positional information can be detectedaccurately enough by using the sync mark detected and/or the precisionpositioning mark detected. Also, in this case, the location of theprecision positioning mark to be detected can be narrowed accurately byusing the sync mark detected. As a result, the writing start and endpoints can be set much more accurately and the positional informationcan be read far more reliably.

Also, in the optical disk medium of the present invention, thepositional information and sync mark are recorded by changing the wobblepattern of the groove. On the other hand, the precision positioning markis formed (e.g., as a mirror mark) so as to have a different grooveshape from that representing the positional information recorded. Thus,the sync mark and the precision positioning mark are easilydistinguishable from each other. As a result, by using the detectionresults of the sync and precision positioning marks in combination asdisclosed for the inventive method and apparatus for reading positionalinformation and the inventive method and apparatus for writing data, thepositional information can be read out and the data can be writtenhighly accurately.

On an optical disk medium according to the present invention, positionalinformation and other types of information are recorded during themanufacturing process thereof by combining a plurality of wobblepatterns of the track groove. Thus, there is no need to provide anyoverhead for recording the positional information for a particular areaof the track groove. In addition, according to the present invention,the wobble as represented by the track groove is displaced at a singlefrequency. Thus, a stabilized clock signal can be easily generated.

Thus the present invention provides an optical disk medium on whichinformation is can be stored at a high density.

While the present invention has been described with respect to preferredembodiments thereof, it will be apparent to those skilled in the artthat the disclosed invention may be modified in numerous ways and mayassume many embodiments other than those specifically described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention that fall within the true spirit andscope of the invention.

What is claimed is:
 1. An optical disk which comprises a track grooveand on which information is recorded along the track groove, wherein thetrack groove includes a plurality of unit sections that are arrangedalong the track groove and that have side faces displaced periodicallyalong the track groove, and wherein the side faces of the unit sectionsare displaced in a single fundamental period, and wherein subdividedinformation allocated to each said unit section is represented by acombination of wobble patterns selected from multiple types of wobblepatterns that have been defined so as to correspond to respective signalwaveforms that rise and fall mutually differently.
 2. The optical diskof claim 1, wherein the subdivided information allocated to each saidunit section is represented by either a first displacement shape or asecond displacement shape, the first displacement shape having beendefined so as to correspond to a signal waveform that rises relativelysteeply and falls relatively gently, the second displacement shapehaving been defined so as to correspond to a signal waveform that risesrelatively gently and falls relatively steeply.
 3. The optical disk ofclaim 1, wherein the side faces of the track groove are displaced eithertoward disk inner periphery or disk outer periphery with respect to acenter-line of the track groove.
 4. The optical disk of claim 1, whereinthe information is recorded on a block-by-block basis, each said blockhaving a predetermined length, and wherein each said block comprises anumber N of unit sections that are arranged along the track groove. 5.The optical disk of claim 4, wherein part of the side faces that isshared by at least two of the unit sections has a constant displacementperiod within at least one of the blocks.
 6. The optical disk of claim1, wherein one-bit subdivided information is allocated to each said unitsection, and wherein a group of subdivided information representing Nbits is recorded on the N unit sections that are included in each saidblock.
 7. The optical disk of claim 6, wherein each said N-bitsubdivided information group includes address information of itsassociated block to which the unit sections, where the subdividedinformation group is recorded, belong.
 8. The optical disk of claim 7,wherein each said N-bit subdivided information group includes an errorcorrection code and/or an error detection code.
 9. The optical disk ofclaim 8, wherein the error correction code or the error detection codehas its ability to correct an error of the address information weightedin such a manner that low-order bits of the error correction ordetection code have a relatively large weight.
 10. A method for readingthe address information of each said block from the optical disk asrecited in claim 7, the method comprising the steps of: irradiating theoptical disk with light and generating an electric signal responsive topart of the light that been reflected from the optical disk; generatinga wobble signal, which has amplitude changing with the wobble pattern,from the electric signal; and determining subdivided information, whichhas been allocated to each of the unit sections included in the block,in accordance with the wobble signal and determining the addressinformation based on the subdivided information.
 11. An apparatus forreading subdivided information from the optical disk as recited in claim1, the apparatus comprising: an optical head, which irradiates theoptical disk with light and generates an electric signal responsive topart of the light that been reflected from the optical disk; read signalprocessing means for generating a wobble signal, which has amplitudechanging with the wobble pattern, from the electric signal; andsubdivided information detecting means for determining the subdividedinformation in accordance with the wobble signal.
 12. A method forreading subdivided information from the optical disk as recited in claim1, the method comprising the steps of: irradiating the optical disk withlight and generating an electric signal responsive to part of the lightthat been reflected from the optical disk; generating a wobble signal,which has amplitude changing with the wobble pattern, from the electricsignal; and determining the subdivided information in accordance withthe wobble signal.